One hundred sixty patients with grade 1 transitional-cell carcinoma of the bladder were evaluated and treated at the Massachusetts General Hospital, Boston. The mean follow-up period was 57 months. There were 92 new patients and 68 patients who had a history of transitional-cell carcinoma. Fifty-three patients (33%) never had another transitional-cell carcinoma. Sixty-eight (43%) of the remaining 107 patients had recurrent Ta grade 1 transitional-cell carcinoma. In 32 patients (20%) disease progressed in grade, in seven patients (4%) invasive transitional-cell carcinoma developed, five patients underwent cystectomy, and one patient died of transitional-cell carcinoma. High-risk factors included positive results of cytologic studies after therapy and three or more recurrences. Multiple therapies were used, but it is impossible to determine if anything other than transurethral resection altered the course in these patients. The data suggest that patients with low-risk factors and Ta grade 1 tumors might be followed up with a quarterly cytologic examination and cystoscopy once or twice a year, unless a change in symptoms occurs.