Objective: To analyze time-trends in age at disability milestones among MS patients who were enrolled into the MSBase International Registry during 1996-2010 period. Methods: We used linear regression to describe the relationship between mean age at major EDSS benchmarks and calendar time. We then assessed time-trend in age at initial EDSS rating with a three level linear growth model specifying that patients were nested within each of 20 participating countries. The model estimated the average of time-trends in mean age at initial clinical assessment within each country while controlling for patients' EDSS and sex in each country. Analyses were repeated in subsamples of patients diagnosed according to Poser or McDonald criteria. Results: The MSBase Registry contained data on 11,108 MS patients enrolled between 1996 and 2010 who fulfilled our inclusion criteria. During the 1996-2010 period, enrollment age for patients with EDSS 4/4.5 increased by 7.9 years, from 43 to 51 years (p < 0.001), and for EDSS 6/6.5 - by 4.9 years, from 48 to 53 year (p < 0.001). These trends were consistent across 20 investigator countries and were observed in Poser-diagnosed as well as McDonald-diagnosed patient subsets. Conclusions: The more recent MSBase enrollees in each of the mild-to-moderate disability strata were significantly older than earlier enrollees. Possible explanations for this phenomenon are discussed.