Forty-one patients (16 females and 25 males) over 10 years of age from five different European centres were studied retrospectively. Of those patients 19 were below the 3rd percentile for height. Hypoglycaemia was still reported in 6 patients. Hepatomegaly was present in 39 out of 40, while 11 out of 27 reported patients had marked hepatomegaly (>10 cm below the costal margin in the midclavicular line). Adenomas were detected in 11 out of 39 patients, -1-fetoprotein was reported to be within normal limits in a total of 22 patients of whom 6 had adenomas. Blood cholesterol concentration was elevated in 31 out of 38 patients, in 7 greater than 10.0 mmol/l. Blood triglycerides were elevated in 29 out of 34 patients, in 8 patients greater than 4.0 mmol/l. Blood uric acid concentration was elevated in 19 out of 35 patients, 12 of them being treated with allopurinol. Mental development was reported to be normal in 32 out of 37 patients. Since limited information on treatment was available no significant differences between treatment groups could be detected. In order to evaluate the effect of treatment, 20 patients (10 females and 10 males) of one centre were studied before and after at least 5 years of treatment. This treatment consisted of frequent feedings during the day together with nocturnal gastric drip feeding. Patients were divided into responders (n=16) and non-responders (n=4) depending on their (change in) SDS (standard deviation score) for height. Liver adenomas were detected in 3 patients, of which one was a non-responder. Alpha-fetoprotein was normal in all patients. With increasing age a gradual increase in blood lipids and some apolipoproteins could be detected, non-responders tending to have higher concentrations of triglycerides, cholesterol, Apo-CIII and Apo-E. Non-responders had significantly higher fasting blood lactate and nocturnal urinary lactate concentrations. Virtually all patients had abnormally elevated glomerular filtration rates, but no significant difference was found between responders and non-responders. Older patients may develop normochromic anaemia. Thrombocyte aggregation was abnormal in 4 out of 16 patients, of which one was a non-responder.