Emphasis is placed on the minor degree of caliectasis often observed in the presence of severe renal failure in patients with retroperitoneal fibrosis. This finding may suggest the diagnosis in individuals presenting with obscure causes of renal failure. A possible explanation for this is based upon an interference with ureteral dynamics and subsequent interference with normal ureteral peristaltic activity rather than mechanical obstruction of the ureter per se. Patients (21) with retroperitoneal fibrosis are reported with the usual sex and age distribution (mostly male, aged 40-55 yr). Two of the patients were interesting because of associated cardiac disease and 3 had been on prolonged methysergide therapy for migraine headaches. Eighteen patients were improved or cured and 3 died.