Objective To examine the effectiveness of a family based grief counselling programme to prevent complicated grief among first degree relatives and spouses of someone who had committed suicide. Design Cluster randomised controlled trial with follow-up at 13 months after the suicide. Setting General practices in the Netherlands. Participants 122 first degree relatives and spouses of 70 people who committed suicide; 39 families (68 participants) were allocated to intervention, 31 families (54 participants) to control. Intervention A family based, cognitive behaviour counselling programme of four sessions with a trained psychiatric nurse counsellor between three to six months after the suicide. Control participants received usual care. Main outcome measures Self report complicated grief. Secondary outcomes were the presence of maladaptive grief reactions, depression, suicidal ideation, and perceptions of being to blame for the suicide. Results The intervention was not associated with a reduction in complicated grief (mean difference -0.61, 95% confidence interval -6.05 to 4.83; P = 0.82). Secondary outcomes were not affected either. When adjusted for baseline inequalities, the intervention reduced the risk of perceptions of being to blame (odds ratio 0.18, 0.05 to 0.67; P = 0.01) and maladaptive grief reactions (0.39, 0.15 to 1.01; P = 0.06). Conclusions A cognitive behaviour grief counselling programme for families bereaved by suicide did not reduce the risk of complicated grief or suicidal ideation or the level of depression. The programme may help to prevent maladaptive grief reactions and perceptions of blame among first degree relatives and spouses