With the use of life tables to describe time while patients were well and subsequent rates of relapse for 75 patients after their recovery from an episodes of major depressive disorder in naturalistic study, a high risk of relapse was detected shortly after recovery. Twenty-four percent of patients relapsed within 12 weeks at risk, and 12% of patients relapsed with four weeks at risk. The presence of an underlying chronic depression and three or more previous affective episodes predicted a statistically significant increase in the rate of relapse. These data were used to develop an exponential model of relapse probability for a subgroup of the study population.