Background Women's groups using participatory methods reduced newborn mortality in rural areas of low income countries. Our study assessed a participatory women's group intervention that focused on women's health, nutrition and family planning.

Methods The study was conducted in three districts in Bangladesh between October 2011 and March 2013, covering a population of around 230 000. On the basis of allocation for the preceding cluster randomised trials, three unions per district were randomly allocated to receive a women's group intervention and three per district were control clusters. Outcomes included unmet need for family planning, morbidity, dietary diversity, night blindness, healthcare decision-making and knowledge of sexual and reproductive health, nutrition and anaemia. A difference-in-difference analysis was used to adjust for secular trends and baseline differences between women taking part in the intervention and a random sample from control clusters.

Results We interviewed 5355 (91% response rate) women before the intervention and 5128 after (96% response rate). There were significant improvements in women's dietary diversity score (increase of 0.2 (95% CI 0.1 to 0.3)) and participation in healthcare decision-making (proportion increase (95% CI) 14.0% (10.6% to 17.4%)). There were also increases in knowledge about: contraception (4.2% (2.0% to 6.3%)), ways to treat (55.4% (52.2% to 58.5%)) and prevent (71.0% (68.0% to 74.1%)) sexually transmitted infections, nutrition (46.6% (43.6% to 49.6%)) and anaemia prevention (62.8% (60.9% to 64.6%)). There were no significant differences in unmet need for family planning, morbidity or night blindness.