Mental disorders contribute to high rates of sickness absence (SA) and impaired work functioning. The aim of the present study was to evaluate the efficacy of 3 interventions targeting SA of workers. Participants (n = 352; 78.4% females) of working age with current employment, and SA due to depression, anxiety disorders, or exhaustion disorder, were recruited to the study and randomized to (a) acceptance and commitment therapy (ACT), (b) a workplace dialogue intervention (WDI), (c) a combination of ACT and WDI, or (d) treatment as usual (TAU). For SA days, there was a significant interaction effect for the follow-up period, in which ACT + WDI generated more SA compared with TAU. When diagnostic group was included as a moderator, participants with exhaustion disorder had less SA days in the WDI group compared with TAU. For symptoms of depression, anxiety, and stress-related ill health, there were significant interaction effects for ACT and ACT + WDI, when compared with TAU, from pre- to postmeasurement (small to moderate between-groups effect sizes). Within-group effect sizes pre- to postmeasurement (Cohen’s d) ranged from .55 to 1.17 (ACT), .40 to .94 (WDI), .26 to 1.13 (ACT + WI), and −.06 to .70 (TAU). There were no differences between groups during follow-up for symptoms.