The reciprocal influence of lupus nephropathy on the outcome of pregnancy and of pregnancy on the course of renal involvement was studied retrospectively in a series of 106 pregnancies observed during the past two decades in 36 patients with lupus nephropathy. The overall incidence of live births, corrected for induced abortions, was 54 (84%) in 64 pregnancies that began before clinical onset of systemic lupus erythematosus (SLE), 20 (87%) in 23 pregnancies that began after onset of SLE, and only four (57%) in seven cases where SLE was first manifested during or after gestation. Relapse or exacerbation of disease activity occurred in 12 (46%) of 26 pregnancies antedated by clinical onset of SLE, more frequently during gestation than post partum, with two cases (8%) of irreversible deterioration of renal function; clinical exacerbation of lupus disease was observed in 11 (66%) of 15 cases where SLE was clinically active at the time of conception, and in only one (9%) of 11 cases where SLE nephritis was in stable clinical remission for at least five months before conception. The data indicate that successful outcome of pregnancy may be expected even in the more severe forms of lupus nephritis if gestation begins after a sustained, complete clinical remission.