Background: Psychological therapies provided in primary care are usually briefer than in secondary care. There has been no recent comprehensive review comparing their effectiveness for common mental health problems. We aimed to compare the effectiveness of different types of brief psychological therapy administered within primary care across and between anxiety, depressive and mixed disorders. Methods: Meta-analysis and meta-regression of randomized controlled trials of brief psychological therapies of adult patients with anxiety, depression or mixed common mental health problems treated in primary care compared to primary care treatment as usual. Results: Thirty-four studies, involving 3962 patients, were included. Most were of brief cognitive behaviour therapy (CBT; n = 13), counselling (n = 8) or problem solving therapy (PST; n = 12). There was differential effectiveness between studies of CBT, with studies of CBT for anxiety disorders having a pooled effect size [d -1.06, 95% confidence interval (CI) -1.31 to -0.80] greater than that of studies of CBT for depression (d -0.33, 95% CI -0.60 to -0.06) or studies of CBT for mixed anxiety and depression (d -0.26, 95% CI -0.44 to -0.08). Counselling for depression and mixed anxiety and depression (d -0.32, 95% CI -0.52 to -0.11) and problem solving therapy (PST) for depression and mixed anxiety and depression (d -0.21, 95% CI -0.37 to -0.05) were also effective. Controlling for diagnosis, meta-regression found no difference between CBT, counselling and PST. Conclusions: Brief CBT, counselling and PST are all effective treatments in primary care, but effect sizes are low compared to longer length treatments. The exception is brief CBT for anxiety, which has comparable effect sizes