An experimental study on the correlation between functional and morphologic recovery of crushed sciatic nerves was carried out in rats. The sciatic nerve of 33 rats, divided into three groups, was submitted to controlled crushing injury on a 5-mm long segment, in a universal testing machine for 10 min with three different loads (100, 500, and 15,000 g, respectively). Functional recovery was evaluated, using a modified sciatic functional index (SFI) at weekly intervals up to the 60th postoperative day, at which time, the animals were sacrificed for histologic and morphometric studies of the nerves. Results were compared with those of normal untouched nerves and nerves submitted to segmentary resection without repair. Initial loss of function was observed in all animals with crush injury, but recovery to a nearly normal SFI occurred after progressively longer intervals (25, 39, and 53 days), as a function of load. Nerve-fiber density was increased in the groups submitted to lower loads, but statistically significantly decreased in the animals submitted to the 15,000-g crush. The authors conclude that the SFI is directly correlated with nerve-fiber density and, therefore, is an adequate tool for evaluating sciatic functional deficiency in the rat.