The aim of this study was to compare the prevalence of antinuclear antibodies (ANA) in very old individuals (>or=86 years of age) with healthy younger (18-68 years) blood donors (n=200) regarding gender, health status, ratio of circulating CD4/CD8 cells and cytomegalovirus (CMV) serology. Frozen plasma was used for ANA detection in two study groups, i.e. 'OCTO' (97 persons aged 86-92 years, 65% women) and 'NONA' (136 persons aged 86-95 years, 70% women). OCTO participants were recruited on the basis that they were healthy or moderately healthy according to a selection protocol. No exclusion criteria regarding health status were applied in the NONA sample. The prevalence of ANA was significantly higher in the oldest-old samples compared to blood donors. There was no association between health status and the presence of ANA in the oldest-old. The difference across age was most pronounced in men, with low levels at younger age, whereas the prevalence among the oldest-old men reached similar levels as in women. There were no associations between the presence of ANA and CD4/CD8 ratio or with CMV status in the oldest-old. Our findings confirm an increased prevalence of ANA in the oldest-old, and emphasize the importance of taking gender and age into consideration when evaluating ANA.