Three patients had renal failure due to obstructive nephropathy associated with processes that prevented dilatation of the collecting systems. Thus, various radiologic procedures, including renal sonography, angiography, and isotope renography, all failed to identify an obstructing process. Because of the high index of clinical suspicion, surgical exploration and nephrostomy were performed on each patient. This confirmed the presence of obstructive nephropathy and led to marked improvement of renal function in each case. When renal failure develops in a setting with a high probability of ureteral obstruction, this diagnosis should be vigorously pursued despite normal radiologic results.