Watch and wait after careful surgical treatment and staging in well-differentiated early ovarian cancer. Patients with well-differentiated epithelial ovarian cancer Stages Ia, Ib, Ic, and IIa (FIGO 1976) were observed after surgical treatment without adjuvant therapy. Careful surgical staging was required, and the extent of the staging procedure was assessed in each individual patient. There were 107 patients entered in the study by nine Dutch oncology centers. Of these 107, 21 did not fulfill all of the inlet criteria of the study and were excluded. Central pathologic review was performed in the remaining 86 cases, revealing that there was borderline tumor in seven patients, moderately or poorly differentiated tumor in nine patients, and tumor of nonepithelial histologic cell type in one patient. In two cases, no material for histologic review was available. After exclusion of these 19 cases, 67 patients were further analyzed. None of these 67 patients was lost during the follow-up period that ranged from 19 to 99 months (mean, 50 months). Tumor recurrence was found in four patients after 11, 25, 34, and 34 months of follow-up, all of whom died shortly after diagnosis of the recurrence without satisfactory response to secondary treatment. For the patients who underwent the most extensive staging procedure, disease-free 5-year survival was 100%. For the patients who were inaccurately staged, disease-free 5-year survival was 88%. It was concluded that well-differentiated early stage (Ia-IIa) ovarian cancer carries an excellent prognosis after surgical treatment and complete surgical staging, with the possible exception of patients with Stage Ic disease with malignant peritoneal washings. Furthermore, it was considered that the application of more objective and consistent ways of assessing tumor grade should be encouraged. Surgical staging should be regarded as the golden standard in defining subsets of low-risk patients and should be included and clearly defined in future trials on early ovarian cancer. 