Thirty-one pregnancies and post partum clinical course of 21 women with a diagnosis of primary focal and segmental hyalinosis and sclerosis have been analyzed. Forty-five percent (14) of pregnancies resulted in fetal loss, 39% (12) in premature delivery and 16% (5) in a term infant. Of 17 fetuses for whom birthweight was recorded, 29% (5) were small for gestational age. Maternal renal function deteriorated in 49% (15) of pregnancies, in 13% (4) irreversibly. Three of these patients (15%) subsequently progressed to end-stage renal failure, and one to progressive chronic renal impairment, by the end of follow-up (median 4 years, range 1-25 years). In 74% (23) of pregnancies hypertension was recorded and this frequently developed early (61%) and was severe (45%). Nephrotic range proteinuria developed in 42% (13) of pregnancies. Increased proteinuria was recorded in 22 (17%) pregnancies. It is concluded that pregnancy in women with primary focal and segmental hyalinosis and sclerosis is associated with increased fetal loss and maternal complications.