Objective: Multimorbidity is known for its negative effects on health related functioning. It remains unclear if these effects are stable over time. The aim was to investigate if the relation between single morbidity/multimorbidity and health related functioning is temporary or persistent. Methods: Data were collected as part of the Maastricht Aging Study (MAAS), a prospective study into the determinants of cognitive aging. Participants (n=1184), 24-81 years old, were recruited from a patient database in primary care (Registration Network Family Practices). Morbidity status (i.e. healthy, single morbidity or multimorbidity) and the Short Form Health Survey (SF-36) were both assessed at baseline, at 3- and 6-year follow-up. Results: At baseline but not at 3- and 6-year follow-up, participants with single morbidity reported poorer physical functioning than their healthy counterparts. Multimorbidity was associated with poorer physical functioning at all measurements. Participants with multimorbidity showed a steep decrease in physical functioning between 3- and 6-year follow-up. Multimorbidity appeared to be unrelated to mental functioning. At baseline and at 3-year follow-up, participants who had a change in morbidity status reported poorer physical functioning than their healthy counterparts. Conclusions: Poorer physical functioning that accompanies multimorbidity is persistent and may even increase over time. People, who acquire one or more diseases during the 3-year follow-up, already showed poorer physical functioning at baseline compared to people who remained healthy during these years. Post-hoc analyses, using the SCL-90 as an outcome measure, did show that multimorbidity was related to depressive and anxiety complaints. However, these complaints seem to decline over time.