BACKGROUND: Integration of primary health care is change to bring together inputs, organisation, management and delivery of particular service functions. Integration has been promoted in the health sector to improve the efficiency of health care delivery. The need for integration arose from perceptions that services were fragmented when delivered through separate vertical programmes. Integration is relevant to the health system at various levels, and this review is concerned with integration at the point of delivery. OBJECTIVES: To assess the effects of strategies to integrate primary health care services on producing a more coherent product and improving health care delivery and health status, in relation to service cost, outputs, impact and user acceptability. SEARCH STRATEGY: We searched the Cochrane Effective Practice and Organisation of Care Group specialised register (August 2000), MEDLINE (1966 to September 2000), EMBASE (1988 to September 2000), Socio Files (1974 to September 2000), Popline (1970 to September 2000), HealthStar (1975 to September 2000), Cinahl (1982 to September 2000); Cab Health (1972 to 1999), International Bibliography of the Social Sciences (1970 to 1999), and reference lists of articles. We also searched the Internet and World Health Organization (WHO) library database, hand searched relevant WHO publications and contacted experts in the field. SELECTION CRITERIA: Randomised trials, controlled before and after studies, and interrupted time series analyses of integration strategies in primary health care services. Health services in high-income countries were excluded. The primary outcomes were service outputs: productivity and coverage, impact, user acceptability and unit cost. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. MAIN RESULTS: Four studies were included. There was no consistent pattern of benefit. Integration had a clear positive effect on the outputs in only one study; in another it had similar effects to vertical programme delivery but greater effect than the control group. In the other two studies integration resulted in negative outputs in comparison with vertical programmes, although in one of these integration performed better than the control group. REVIEWER'S CONCLUSIONS: Few studies of good quality, large and with rigorous study design have been carried out to investigate the evidence to support integration as a style of service delivery. In fact, some studies found greater effects for vertical health care delivery. Policy makers and planners considering integration could introduce strategies, using rigorous study design, to allow further evaluation and increase the base of studies from which to draw evidence.