To describe the clinical and neurophysiological spectrum and prognosis in a large cohort of biochemically and genetically proven late onset Pompe patients. Thirty-eight diagnosed with late onset Pompe disease at our neuromuscular department during 1985 and 2006 are described in detail. The mean delay from onset of symptoms or first medical consultation until diagnosis was 10.4 and 7.1 years, respectively. A different diagnosis was suggested in 11 of 38 patients. Ten patients underwent repeated muscle biopsies before diagnosis of Pompe disease was established. Limb girdle weakness was the most frequent presenting sign. Six patients complained of myalgia. Wolf-Parkinson-White syndrome was found in 3 of 38 patients. Respiratory failure preceded the onset of overt limb muscle weakness in three patients. The course of the patients was progressive in all, but there was a wide variety of progression, which did not correlate with the age of disease onset. In 71% of the patients, neurophysiological investigations revealed a myopathic EMG pattern, half of the patients had spontaneous activity including complex repetitive discharges. A normal EMG was found in 9% of the patients. Nerve conduction studies were normal in all. Pompe disease should be taken into consideration in patients with unexplained limb girdle muscular weakness with respiratory failure. Cardiac manifestations may not be restricted to infantile Pompe disease.