Insulin resistance have been demonstrated in untreated patients with Gaucher type I disease. It was implied in overweight enzyme replacement therapy (ERT) treated patients with Gaucher type I disease. In present study we investigate whether insulin resistance is presented in fourteen ERT treated patients with Gaucher type I disease and without overweight in comparison to normal subjects. This work illustrates the presence of insulin resistance in non-overweight ERT treated patients with Gaucher type I disease.