There is need for more knowledge about the relationship between work and cognitive functioning in sick-listed individuals. This study investigated whether the degree of work participation is relevant for recovery of cognitive functioning in sick-listed individuals. 177 occupational rehabilitation participants and 70 controls participated in a non-randomised, longitudinal study. Participants completed computerised cognitive tests targeting sustained attention and working memory at start and end of rehabilitation and 3 and 12 months after rehabilitation. The change score performance in attention and memory between start and end, start and 3 months and 12 months was compared in individuals on sick leave 100-75%, 74-40% and 39-0% (three sick leave groups) of the time in the year after rehabilitation, and a control group not being on sick leave. Fixed effect analysis of covariance adjusting for education and work ability was used. The sick leave group 100-75% had significantly lower score on work ability compared to the other groups at baseline. The main findings indicated that the sick leave group 39-0% improved significantly more in sustained attention compared to the sick leave group 100-75% between start and end of rehabilitation and from start of rehabilitation to 3 and 12 months after. The degree of work participation seems relevant to recovery of the cognitive function sustained attention in sick-listed individuals. These findings encourage work rehabilitation clinicians, work consultants and employers to develop RTW plans which take into account that graded employment influence cognitive functioning.