The diagnosis of nonpigmented endometrial lesions by simple laparoscopic visualization is difficult and often inaccurate. We therefore sought to establish a new and more accurate method to visualize these nonpigmented peritoneal changes caused by endometriosis.A total of 37 patients received 30 mg 5-aminolevulinic acid/kg body weight 10 to 14 hs prior to surgery. Laparoscopy was then performed using a D-light system (Storz, Tuttlingen, Germany). The findings were evaluated first in the white-light mode; the D-light system was then activated, and all areas of fluorescence were documented. Multiple specimens were obtained by biopsy.The sensitivity of the fluorescence diagnosis in detecting endometriosis in nonpigmented areas and normal-looking peritoneum is 100%, with a specificity of 75%. Diagnosis by simple visualization under white illumination has a sensitivity of only 69% and a specificity of 70%. Occult areas of endometriosis were discovered using fluorescence diagnosis.Our findings suggest that fluorescence diagnosis using 5-aminolevulinic acid is feasible and can improve the diagnosis of endometriosis in nonpigmented and occult endometrial lesions. Fluorescence diagnosis is a promising new tool in the diagnosis of endometriosis.