Short-term hypothyroidism has been associated with a reversible rise in serum creatinine levels in patients with normal renal function. A remarkable decline in serum creatinine levels associated with a treatment of severe and prolonged hypothyroidism has rarely been reported so far. We present here 2 patients with chronic renal failure in whom treatment for hypothyroidism resulted in a significant and sustained reduction of their serum creatinine levels. These cases indicate that because hypothyroidism may aggravate the serum creatinine levels, TSH should be considered in screening procedures of patients with chronic renal failure presenting with recent accelerated aggravation of renal function. Hypothyroidism per se, one of its complications or one of its associated autoimmune diseases might play a role in modifying the underlying renal problem.