The aim of this study was to investigate the incidence of limitations in self-reported mobility as well as the decline in measured walking speed and stair-mounting ability over five years among men and women aged 75 at baseline in two Nordic localities. Another purpose was to analyze the relationship and its consistency over time between self-reports and performance-based measures in the decline of mobility. Identical Interviews and performance tests were carried out in Jyäskylä, Finland (N=244) and Glostrup, Denmark (N=275) at baseline and five years later. The subjects were asked about their ability to manage with transferring from chair or bed, walking indoors and outdoors and climbing stairs. The occurrence of new limitations in these tasks was analyzed among those who did not report limitations in the same task at baseline. Maximal walking speed and step-mounting height were measured in the laboratory. The decline in walking speed below 1.2 m/s and stair-mounting height below 30 cm was analyzed among those whose results were, initially, above these limits. Most frequently, new limitations occurred in walking outdoors and in climbing stairs (44-60%). Walking speed and stair-mounting ability deteriorated below the thresholds mentioned in 4-36% of the participants, depending on gender and locality. There were only minor differences between the two Nordic localities in the decline in mobility functions. A substantial proportion of those whose performance had declined had developed limitations in self-reported mobility as well. However, the relationship between different methods of measurement was not straightforward. This indicates that multiple approaches are needed to obtain thorough knowledge about mobility and its decline among elderly people.