This thesis concerns health and functional status in old age, as well as older adults' attitudes towards research participation. Five studies were performed using data from the Kungsholmen Project, a population-based study on ageing and dementia ongoing in Stockholm since 1987.

Occurrence of dementia. Both prevalence and incidence of dementia were investigated. In the 75-79 age group the incidence rates for dementia were 19.6 for women and 12.4 for men per 1,000 person-years, whereas the corresponding figures were 86.7 and 15.0 among 90+ year old subjects. A prevalence study with an enlarged sample of nonagenarians showed that the probability of having dementia after the age of 75 increased by 10% each year and 90% every 5 years. AD contributed to 76. 5% and VaD to 17.9% of the prevalent cases.

Health and functional status. Higher morbidity prevalence in women than in men was detected only after the age of 85. 90+ year old women compared to men had an OR=2.2 (95% CI 1.1-4-3) for disability after adjustment for age, education, and number of diseases. Functionally independent men in the youngest age group had a higher risk of death than women (OR=0.4; 95% CI 0.3-0.7), whereas no gender difference was found among disabled subjects. Incidence of long term disability in women was higher than in men only in the 90+ years old subjects, although the difference was not statistically significant after adjustment.

Effects of research. In a postal questionnaire, 79% of the subjects reported advantages in research participation. Older elderly with impaired cognitive functioning and lower education showed the least positive attitude. The first contact and the cognitive testing were judged as the most stressful situations. Community-based longitudinal surveys also appear to have a social function, thus stressing ethical issues regarding the termination of contact when studies are completed.

Conclusions. The dementia incidence increases with age, even in the most advanced ages. This increase is especially evident among women, leading to an increased risk of dementia in the male gender. A large proportion of nonagenarians were functionally independent (73%) despite their advanced age, and 19% had no diseases at all. The gender distribution of morbidity, mortality and disability was modified by age. 90+ year old women were more disabled than men, partially due to the excess of dementia and other chronic diseases. We hypothesise that more women may be at higher risk of developing severe disability than men in the advanced ages due to a longer survival of women with slight disability in earlier ages.

Finally, this thesis provides empirical data concerning the impact of longitudinal research on participants that may help researchers in lowering the refusal rate in epidemiological studies, and might assist ethics committees in making their judgements.