The impact of attrition was studied in a two-wave panel study on the associations between psychological attributes (mastery, self-efficacy expectancies) and disability increase among low-functioning older persons (n = 753, 76.4% participated at the follow-up 2 years later). The results showed that: (1) attrition at follow-up was clearly associated with age and level of disability at baseline. Older persons and those with higher levels of disability did not participate in the follow-up; and (2) the strength of the association between the selected psychological attributes and the increase in disability did not substantially alter when (a) missing follow-up scores of disability were replaced by several values (e.g., lower, equal or higher compared to those who actually participated at the follow-up), or (b) associations were computed excluding those participants at follow-up with highest increase in disability. We conclude that attrition may affect the descriptive outcomes of aging studies, particularly when such studies focus on health and function, but that attrition not always seems to be a serious problem when associations between variables are the focus of study.