Sleep disturbances are frequently part of the symptomatology in refugees with post-traumatic stress disorder (PTSD). It has been suggested that targeting sleep disturbances may enhance the outcome of PTSD treatment. However, randomized studies on the effect of treatment focusing on sleep disturbances in refugees with PTSD are lacking. The aim of this study was to examine add-on treatment with imagery rehearsal therapy (IRT) and/or mianserin against treatment as usual (TAU) alone in a sample of trauma-affected refugees with PTSD at 8-12 months follow-up. In a randomized controlled trial, 219 adult refugees diagnosed with PTSD and suffering from sleep disturbances were randomized to four groups (1:1:1:1) receiving, respectively, TAU, TAU + mianserin, TAU + IRT, and TAU + IRT + mianserin. The primary outcome was subjective sleep quality (Pittsburgh Sleep Quality Index) and the secondary outcomes included PTSD and depression symptoms, level of functioning and subjective well-being. The data were analysed using mixed models. The only significant effect of IRT was on level of functioning (p = .040, ES 0.44), whereas there was no significant effect of mianserin on any of the measured outcomes. Low adherence to both IRT (39%) and mianserin (20%) was observed. Contrary to our hypothesis, we did not find IRT or mianserin to be superior to TAU. The low adherence may potentially cause an underestimation of the effect of IRT and mianserin and indicates a necessity to further analyse the complex factors that may impact the motivation and ability of trauma-affected refugees to participate in and profit from available treatment options.