Mutation in genes encoding for proteins involved in glycogen synthesis, degradation or regulation results in various inborn errors of glycogen metabolism. The disorders that result in abnormal storage of glycogen are known as glycogen storage diseases (GSD). We report a rare and interesting case of a young boy who presented with generalized weakness and reduced muscle bulk since childhood. He was diagnosed to have acid maltase deficiency, also known as Pompe's disease, one of the rare types of glycogen storage disease. The case is presented here in the form of a case study, including a review of the pertinent literature on the subject. This case has the potential to be the first reported case of such a disease from Pakistan (to the best of our knowledge).