Polypoidal choroidal vasculopathy (PCV) is characterized by a branching vascular network with polypoidal lesions under the retinal pigment epithelium (RPE). In Japan, it is classified as a specific form of exudative age-related macular degeneration. However, several issues which we investigated regarding the pathogenesis and treatment of PCV remain unresolved. We investigated the pathogenesis, clinical findings and treatment of PCV. 1. Indocyanine green angiographic findings. There were two different patterns on indocyanine green angiograms. In the first pattern, both feeder and draining vessels were visible and network vessels showed characteristic findings of choroidal neovascularization (CNV). Points of focal dilatation on marginal vessels were comprised of polypoidal lesions. In the second pattern, neither feeder nor draining vessels were visible and there were few network vessels. The points of deformation of network vessels appeared to be polypoidal lesions. The former represents a deformation of CNV, i.e. polypoidal CNV; the latter is thought to result from abnormalities of the choroidal vessels, i.e. PCV in the strict sense. 2. Pathological findings of PCV in the strict sense. The histopathological characteristics of PCV in the strict sense, which had been eliminated by vitrectomy, were dilatation and hyalinization of vessels, massive exudative changes in blood plasma, basement membrane-like deposits and scant granulomatous tissue. These vessels were located beneath Bruch's membrane. The findings indicate that PCV in the strict sense arises from hyalinized arteriolosclerosis of choroidal vessels. 3. Optical coherence tomographic findings. A break was found in the high reflective line which revealed Bruch's membrane. Low reflective tissue was observed at the break corresponding to a feeder vessel. The high reflective line which corresponded to the retinal pigment epithelium was uneven, and highly elevated portions of the RPE corresponded to thick network vessels and polypoidal lesions. Feeder vessels are thought to invade via Bruch's membrane to form network vessels and polypoidal lesions at the termini of the network vessels, both of which push the RPE upward. Therefore, polypoidal CNV is thought to represent a deformation of the CNV under the RPE. In PCV in the strict sense, an irregular thickened line with highly reflective substances adhering to the lower portion of it, curved downward corresponding to the site at which the network vessel filling began. A dimple in the RPE was observed which paralleled the curve of the line. The RPE was pushed upward, corresponding to the network vessels. Judging from the results of histopathological studies, abnormal vessels may be pushed up the RPE secondary to an increase in intravascular pressure due to the presence of several dilated vessels and by massive exudation from these vessels within the choroid at network vessels. The dimple in the RPE might be attributable to intra-choroidal pressure being decreased at the point at which network vessel filling began. 4. Genetic findings. There were significant differences in all distributions of ARMS 2 (A69S) between the polypoidal CNV and control groups. In contrast, the distribution of ARMS 2 (A69S) did not differ between the PCV in the strict sense group and the control group. The ARMS 2 (A69S) gene is closely related to age-related macular degeneration. Polypoidal CNV was thought to be associated with age-related macular degeneration. 5. Treatment of subfoveal PCV. Mean visual acuity improved 1 year after photodynamic therapy (PDT). Good visual acuity, small lesion size of the network of vessels with polypoidal lesions, and the absence of subfoveal polypoidal lesions were pre-PDT predictors that corresponded to the improvement in vision. However, mean visual acuity had decreased to a level similar to that prior to PDT at 2 and 3 years after treatment. In PCV in the strict sense, the branching vascular network persisted after PDT, and polypoidal lesions frequently recurred at the termini. The branching vascular network sometimes expanded and was accompanied by polypoidal CNV or classic CNV. These results indicate that repeated PDT, as monotherapy, has limitations as a long-term treatment for PCV in the strict sense. Intravitreal injection of ranibizumab for eyes with a visual acuity of 0.6 or more, which is not a good indication for PDT, achieved improvement in mean visual acuity 1 year after the treatment, though the frequency of polypoidal lesion regression was low. This procedure seems to be useful for eyes with good visual acuity for a period of at least one year. 6. Conclusion. Using indocyanine green angiography, optical coherence tomography and genetic testing, PCV was classified into 2 groups, polypoidal CNV and PCV in the strict sense. PCV in the strict sense was characterized by arteriolsclerosis histopathologically. Polypoidal CNV is thought to represent deformation of CNV under the RPE in age-related macular degeneration, while PCV in the strict sense is thought to be due to choroidal vessel abnormalities. The long-term efficacy of repeated PDT as monotherapy, for subfoveal PCV was limited. Further evaluation is necessary to establish a treatment algorithm for PCV.