The classic clinical presentation for type IV glycogen storage disease (branching enzyme deficiency, GSD IV) is hepatosplenomegaly with failure to thrive occurring in the first 18 months of life, followed by progressive liver failure and death by age 5 years. Although there have been two patients without apparent liver progression previously reported, no long-term follow-up clinical data have been available. We present here the clinical spectrum of the non-progressive liver form of GSD IV in four patients, and long-term follow-up of the oldest identified patients (ages 13 and 20 years). None has developed progressive liver cirrhosis, skeletal muscle, cardiac or neurological involvement, and none has been transplanted. Branching enzyme activity was also measured in cultured skin fibroblasts from patients with the classic liver progressive, the early neonatal fatal, and the non-progressive hepatic presentations of GSD IV. The residual branching enzyme activity in the patients without progression was not distinguishable from the other forms and could not be used to predict the clinical course. Our data indicate that GSD IV does not always necessitate hepatic transplantation and that caution should be used when counselling patients regarding the prognosis of GSD IV. Patients should be carefully monitored for evidence of progression before recommending liver transplantation.