Secondary polycythaemia associated with unilateral renal cystic disease.

Unilateral renal cystic disease (URCD) is a rare condition, with pathological features indistinguishable from autosomal dominant polycystic kidney disease (ADPKD). In contrast to this condition, however, URCD is not inherited, is not associated with progressive deterioration in renal function, and is unilateral. We present a case of URCD associated with polycythaemia, which showed resolution following nephrectomy. Secondary polycythaemia has not previously been reported in cases of URCD, but may be hypothesised to be a result of excess erythropoietin production.