Between January 1985 and July 1989 we diagnosed asymptomatic stage I multiple myeloma according to Durie and Salmon [Durie and Salmon: Cancer 36:842, 1975] in 91 patients. All patients were followed without chemotherapy. Disease progression occurred in 41 patients and the median time to progression for all patients was 48 months. In the Cox multivariate regression analysis, hemoglobin levels < 12 g/dl (P < .01), bone marrow plasmacytosis > 25% (P < .01), and M-component size > or = 30 g/l for Ig G or > or = 25 g/l for Ig A (P < .01) were the only significant prognostic factors for progression. The 38 patients without any harmful factor remained free of progression for a median of more than 50 months. The 18 patients with two or three of these characteristics (high-risk group) had the shortest median time to progression of 6 months. Despite different times to progression, the response rate and survival after chemotherapy were similar for all groups of patients. Patients in the high-risk group for progression have to be frequently monitored for disease progression and might benefit from early treatment.