Fifty-two untreated patients with late-onset Pompe disease completed questionnaires about their clinical condition and level of handicap at baseline and at 1-year (n = 41) and 2-year follow-ups (n = 40). During this period, declines in functional activities, respiratory function, handicap, and survival were recorded on a group level. This study illustrates the progressiveness of late-onset Pompe disease and indicates the need for close clinical follow-up of both children and adults with this disorder.