Anatomical resections of the segment, so called 'anatomical segmentectomy', involving a small-sized lung cancer performed in 55 compromised cases in our hospital since 1985. On the operation we separated the intersegmental plane not with the traditional digital dissection but with meticulous electrocautery following the intersegmental pulmonary venous structure from hilal towards the peripheral area. Forty-six cases were primary lung cancers and 9 were metastatic ones. In 7 cases cancer residue was confirmed, especially on the intersegmental plane in one case and on the bronchial stump in another one. In 35 cases of primary non-small cell lung cancer (NSLC), recurrences in the separated plane or other segment of the same lobe appeared later in 2 cases, however there was no locoregional recurrence in cases with tumorous diameter less than 30 mm. The prognosis of 29 cases of NSLC with p-stage I is excellent because those 5 year survival rate is very high, 87.1%. The mean loss of ventilatory functions after segmentectomy was approximately half that of lobectomy. According to these results, we conclude that the anatomical segmentectomy is useful to the limited resection for small-sized NSLC with stage I.