OBJECTIVE: To analyze whether functional decline from age 80 to 85 is influenced by changes in self-reported tiredness in daily activities in the preceding 5-year period. METHOD: A prospective study of 226 75-year-old men and women with 5- and 10-year follow-up in the Western part of Copenhagen County. Tiredness in daily activities was measured at age 75 and 80 by a validated scale. Changes in tiredness from age 75 to 80: 1) Sustained no tiredness, 2) not tired-tired, 3) tired-not tired, 4) sustained tiredness. Functional decline from age 80 to 85:1) Sustained no need of help; 2) need of help at age 85, alive; 3) need of help at age 85 or dead; 4) dead. RESULTS: The analyses among the survivors showed a slight tendency to an association between having sustained tiredness or development of tiredness from age 75 to 80 and functional decline from age 80 to 85. Persons with sustained tiredness from age 75 to 80 were at significantly larger risk of functional decline and mortality from age 80 to 85. These results were not attenuated when adjusted by the covariates. CONCLUSION: The results in the present study indicate that it is important to take continuous complaints about tiredness in daily activities seriously, because this is an early sign of functional decline.