Muscle phosphofructokinase deficiency is known to cause childhood-onset exercise intolerance, muscle cramps, and myoglobinuria. Rarely, phosphofructokinase deficiency manifests in infancy as congenital myopathy and arthrogryposis with fatal outcome. Here, the authors report the case of a 2-year-old boy with infantile phosphofructokinase deficiency who presented on the third day of life with intractable seizures. Two of his sisters died in infancy with hypotonia, developmental delay, and seizure disorder of unclear etiology. On follow-up, he has had hypotonia and mild developmental delay. However, he continues to gain developmental milestones, and his seizures are now well controlled on carbamazepine. This presentation suggests expanding the phenotype of muscle phosphofructokinase deficiency to include early-onset neonatal seizures. It is also unusual in the relatively milder course of the infantile form of this disorder. The authors propose that this form of glycogen storage disease be considered in the differential diagnosis of neonatal seizures and early infantile nonprogressive muscle weakness.