Seventeen patients with lung metastases from colorectal cancer underwent intraoperative pleural lavage cytology immediately after thoracotomy from August 1988 to December 1994. Patients with pleural effusion and/or dissemination were excluded. The median followup period was 34 months (range 3-52 months). Of the 17 patients, 13 were cytologically negative (76%, group A) and 4 were positive (24% group B). Recurrence rate in the pleural cavity was 25% (1/4) in group B and 0% (0/13) in group A. The three-year survival rate was 0% in group B and 78% in group A, respectively. These results indicate that intraoperative pleural lavage cytology is useful in the assessment of prognosis, and locoregional therapy should be considered for cytology positive group.