Background: Reducing the worldwide mortality ratio by 75 per cent between 1990 and 2015 is a key Millennium Development Goal. Randomized controlled trials (RCTs) are the accepted 'gold standard' to assess the effectiveness of interventions but they are not always appropriate for practical, ethical or economic reasons in developing countries. This study examines the use of cluster randomized trials and quasi-experimental (nonrandomized) study designs to evaluate complex interventions implemented to reduce maternal mortality. Methods: We systematically searched electronic databases including MEDLINE, EMBASE, CINAHL, BNI, ASSIA, IBSS, CSA and COCHRANE. English language publications between 1990 and 2003 were included. Studies that assessed the effects of complex interventions aimed at reducing maternal mortality in developing countries were included. Results: Four cluster randomized trials and eleven quasi-experimental studies were identified. Two cluster randomized trials examined reduction in prenatal visits with no adverse effects on maternal mortality. Two trials assessed the effects of vitamin A supplementation. Both trials found a significant reduction in maternal mortality ratios after vitamin A supplementation. A decline in maternal deaths was reported in eight of the nonrandomized studies. Measuring maternal mortality was a frequent problem because of insufficient sample sizes and/or poor recording methods. Other limitations include lack of suitable comparison groups and difficulties assessing the effects of confounding factors in the quasi-experimental studies. Conclusions: RCTs may not be appropriate to evaluate complex interventions in maternal mortality and cluster RCTs and quasi-experimental designs may be more suitable. However, further work is required to improve the robustness of such alternative study designs.