Type I Gaucher disease, a lysosomal storage disorder is associated with metabolic abnormalities such as high resting energy expenditure, low circulating adiponectin and peripheral insulin resistance. Treatment with enzyme replacement therapy (enzyme therapy) leads to a decrease in resting energy expenditure, but its influence on weight and risk of development of type II diabetes is unknown. We studied the BMI, prevalence of overweight, insulin resistance and type II diabetes in untreated and enzyme therapy treated Gaucher patients before and after several years of follow-up and compared this to data on healthy subjects from literature. We established that in untreated Gaucher patients the prevalence of overweight is lower than in the general population. Long-term treatment with enzyme therapy induces a larger than average weight gain leading to a similar prevalence of overweight in enzyme therapy treated patients and the general population. The prevalence of type II diabetes increases significantly during treatment with enzyme therapy, resulting in a comparable prevalence of type II diabetes in enzyme therapy treated patients and the general population.