Approximately 20% of patients with multiple myeloma are recognized by chance without significant symptoms. In order to prevent morbidity with timely therapy, reliable criteria are needed that distinguish those likely to show early or late disease progression. Multiple clinical features were assessed in 101 consecutive, asymptomatic and previously untreated patients. Patients with one or more lytic bone lesions were excluded because this feature had been found previously to be associated with early progression. Multivariate analysis indicated that only serum myeloma globulin > 30 g/l, IgA protein type, and Bence Jones protein excretion > 50 mg/d remained as significant independent variables. The presence of two or more of these features signified high-risk disease with early progression (median 17 months) whereas the absence of any adverse variable was associated with prolonged stability (median 95 months) (P < 0.01). Magnetic resonance (MR) imaging of the spine was useful only in patients with one adverse feature and an intermediate time to progression (median 39 months). An abnormal pattern (40% of patients) helped to distinguish patients with an imminent complication from those with more stable disease. Because a serious complication (fracture, hypercalcaemia) occurred in 35% of patients with early disease progression, chemotherapy seems justified for selected patients with asymptomatic disease at diagnosis. The remaining patients were at such low risk for progression (median 6 years) that they may be followed safely at long intervals without treatment.