Adenocarcinomas with a micropapillary pattern (MPP), featuring small papillary tufts lacking a central fibrovascular core, are thought to have a poor prognosis. To examine whether the MPP is a predictor of prognosis, clinicopathologic characteristics of adenocarcinomas were analyzed with particular reference to survival of early-stage patients. The subjects were 344 consecutive patients (female/male ratio 163:181) for whom complete surgical resection was undertaken at the Cancer Institute Hospital, Japan, during 1986-1995. Histologically, they were divided into two groups: MPP-positive (n = 139; 40%) and MPP-negative (n = 205; 60%). The following items were significantly more frequent in the MPP-positive group: metastasis to lymph nodes (p <0.001), pleural invasion (p = 0.02), intrapulmonary metastasis (p <0.001), and nonsmoking status (p = 0.002). In stage I patients (i.e., without lymph node metastasis, n = 154), 5-year survival of the MPP-positive group (n = 45) was 79%, significantly lower than the MPP-negative group (n = 109) of 93% (p = 0.004). In many cases of the c-stage I MPP-positive group, upstaging was necessary on the basis of pathologic findings for metastases, and the survival was between stage I and stage II. Our study clearly indicated that the MPP is a distinct prognostic marker for lung adenocarcinoma, particularly regarding apparent stage I diseases.