The association of a spondyloepiphyseal dysplasia tarda (SED-T) with the nephrotic syndrome (NS) was found in three siblings. They have counsaguineous (first cousins) healthy parents. Patient 1 was a boy who was admitted to hospital for oedema at the age of 8 years; NS was diagnosed, renal biopsy revealed mesangioproliferative glomerulonephritis. After 4 years he developed end-stage renal failure and died whilst on haemodialysis. Combined therapy with cyclophosphamide and prednisone was of no benefit. At the age of 11 years his height was 122 cm (< 3rd percentile -3.2 SD); he had a short neck, broad and prominent chest and a short wide trunk. Patient 2, another male, had non-nephrotic proteinuria in a 24-h urinary sample at the age of 11 years; this was confirmed in a later analysis; mild lymphopenia and a reduction of helper T cell (OKT4)/suppressor T cell (OKT8) ratio was also detected. At 22 years of age he was admitted to hospital with end-stage renal failure. He was on haemodialysis for a few months until his mother donated a kidney. At the age of 22 years his height was 157 cm (< 3rd percentile), he had a short trunk with the thoracic cage increased in anteroposterior diameter and shoulder elevation. Roentgenograms revealed a disostosis of the spinal column and pelvis and a slight lombar platyspondylia. Patient 3, a girl, was admitted to hospital at 12.5 years for pain and restricted mobility of the right hip. X-rays showed deep acetabula and short femoral necks and mild dysplastic changes, especially in the right hip.(ABSTRACT TRUNCATED AT 250 WORDS)