Purpose. People with long-term mental health problems are heavier smokers than the general population, and suffer greater smoking-related morbidity and mortality. Little is known about the effectiveness of psychological smoking cessation interventions for this group. This review evaluates evidence from randomized controlled trials (RCTs) on the effectiveness of psychological interventions, used alone or with pharmacotherapy, in reducing smoking in adults with mental health problems.Methods. We searched relevant articles between January 1999 and March 2019 and identified 6,200 papers. Two reviewers screened 81 full-text articles. Outcome measures included number of cigarettes smoked per day, 7-day point prevalence abstinence, and continuous abstinence from smoking.Results. Thirteen RCTs, involving 1,497 participants, met the inclusion criteria. Psychological interventions included cognitive behavioural therapy (CBT), motivational interviewing (MI), counselling, and telephone smoking cessation support. Three trials resulted in significant reductions in smoking for patients receiving psychological interventions compared with controls. Two trials showed higher 7-day point prevalence in intervention plus nicotine replacement therapy (NRT) versus standard care groups. Four trials showed that participants who combined pharmacotherapy (bupropion or varenicline) with CBT were more likely to reduce their smoking by 50% than those receiving CBT only. Four out of five trials that compared different psychological interventions (with or without NRT) had positive outcomes regardless of intervention type.Conclusions. This study contributes to our understanding in a number of ways: The available evidence is consistent with a range of psychological interventions being independently effective in reducing smoking by people with mental health problems; however, too few well-designed studies have been conducted for us to be confident about, for example, which interventions work best for whom, and how they should be implemented. Evidence is clearer for a range of psychological interventionsincluding CBT, MI, and behavioural or supportive counsellingbeing effective when used with NRT or pharmacotherapy. Telephone-based and relatively brief interventions appear to be as effective as more intense and longer-term ones. There is also good evidence for a strongThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.