BACKGROUND: Mental health problems in children are common. Research suggests that parenting has an important role to play in helping children to become well adjusted adults, and that the first few months and years of a child's life are especially important in establishing patterns of emotional, cognitive and social functioning which will in turn influence the child's future development and in particular, their mental health. Parenting programmes may therefore have a role to play in improving the mental health of infants and toddlers. OBJECTIVES: The objectives of this review are as follows: a) To establish whether group-based parenting programmes are effective in improving the mental health of children less than three years of age b) To assess the role of parenting programmes in the primary prevention of mental health problems SEARCH STRATEGY: A range of biomedical and social science databases were searched including MEDLINE, EMBASE, CINAHL, PsychLIT, Sociofile, Social Science Citation Index, ASSIA, the Cochrane Library including SPECTR, CENTRAL, National Research Register (NRR) and ERIC. SELECTION CRITERIA: Only randomised controlled trials were included and studies had to include at least one standardised instrument measuring some aspect of infant mental health. DATA COLLECTION AND ANALYSIS: The treatment effect for each outcome in each study was standardised by dividing the mean difference in post-intervention scores for the intervention and treatment group, by the pooled standard deviation, to obtain an effect size. The results for each outcome in each study have been presented with 95% confidence intervals. Where appropriate the results have been combined in a meta-analysis using a random effect model. MAIN RESULTS: A total of five studies were included in the review. The 5 included studies provided a total of 36 assessments of infant and toddler mental health including emotional and behavioural adjustment, and sleep patterns. All of the results apart from 6 showed positive findings favouring the intervention group. While some of findings were non-significant, most of the effect sizes were large and the wide confidence intervals crossing the zero that were obtained in a number of the studies, were very probably due to small sample sizes. There was sufficient data from four studies to combine the results in a meta-analysis. The results of the meta-analysis show a significant difference in children's emotional and behavioural adjustment favouring the intervention group. Overall, the limited follow-up data provide equivocal evidence concerning the maintenance of these effects over time. REVIEWER'S CONCLUSIONS: The results of this review suggest that parenting programmes can be effective in improving the mental health of infants and toddlers. There is, however, insufficient evidence to reach any firm conclusions regarding the role that such programmes might play in the primary prevention of mental health problems. Furthermore, there is insufficient evidence to know whether the short-term benefit of these programmes is maintained over time, and further research is required.