Phosphoglycerate mutase (PGAM) deficiency causes a rare metabolic myopathy characterized by exercise-related myalgia and myoglobinuria. This disorder was described in 13 patients and five different mutations in the PGAM-M gene were identified. We report on a new patient with an unusual clinical presentation. As a youth, he participated in different sports without complaining of muscular symptoms, but at 44 years of age, after a brief, intense effort, he experienced lightheadedness without fainting. Serum CK was elevated and the ischemic exercise test showed a pathological lactate response. Muscle biopsy showed only mild abnormalities, but biochemical study revealed a defect of PGAM and genetic analysis showed two different mutations in the PGAM-M gene. Our case expands the clinical spectrum of PGAM deficiency and suggests that the frequency of this metabolic myopathy may be underestimated.