OBJECTIVE: To assess the health benefits of outdoor walking groups. DESIGN: Systematic review and meta-analysis of walking group interventions examining differences in commonly used physiological, psychological and well-being outcomes between baseline and intervention end. DATA SOURCES: Seven electronic databases, clinical trial registers, grey literature and reference lists in English language up to November 2013. ELIGIBILITY CRITERIA: Adults, group walking outdoors with outcomes directly attributable to the walking intervention. RESULTS: Forty-two studies were identified involving 1843 participants. There is evidence that walking groups have wide-ranging health benefits. Meta-analysis showed statistically significant reductions in mean difference for systolic blood pressure -3.72 mm Hg (-5.28 to -2.17) and diastolic blood pressure -3.14 mm Hg (-4.15 to -2.13); resting heart rate -2.88 bpm (-4.13 to -1.64); body fat -1.31% (-2.10 to -0.52), body mass index -0.71 kg/m(2) (-1.19 to -0.23), total cholesterol -0.11 mmol/L (-0.22 to -0.01) and statistically significant mean increases in VO(2max) of 2.66 mL/kg/min (1.67-3.65), the SF-36 (physical functioning) score 6.02 (0.51 to 11.53) and a 6 min walk time of 79.6 m (53.37-105.84). A standardised mean difference showed a reduction in depression scores with an effect size of -0.67 (-0.97 to -0.38). The evidence was less clear for other outcomes such as waist circumference fasting glucose, SF-36 (mental health) and serum lipids such as high-density lipids. There were no notable adverse side effects reported in any of the studies. CONCLUSIONS: Walking groups are effective and safe with good adherence and wide-ranging health benefits. They could be a promising intervention as an adjunct to other healthcare or as a proactive health-promoting activity.