The question of whether initial treatment is necessary in relatively asymptomatic patients with stage III and IV non-Hodgkin's lymphomas of favorable histologic types was studied by retrospective analysis. Two groups of patients were studied:  44 nonprotocol patients, followed since 1963, in whom initial treatment was withheld until required to evaluate the pace of disease and the necessity of treatment; and  112 previously untreated patients who have participated in prospectively randomized clinical trials since 1971. For all 44 “deferred” patients, the median time before requiring treatment was 31 months, and there have been 19 patients who have not yet required therapy for periods of 3 to 104 months. The median actuarial survival for all 44 patients was 121 months. At 4 years, the actuarial survival of the 44 patients with deferred treatment is 77.3%, compared with 83.2% for the 112 protocol patients (P = 0.60). Careful observation without initiation of therapy is an appropriate option in the management of patients with relatively asymptomatic advanced non-Hodgkin's lymphomas of favorable histologic types.