OBJECTIVE To investigate associations between neighbourhood greenspace and weight status, and to explore the contribution of physical activity to these associations. METHODS Cross-sectional observational study over two time-periods. METHODS Participants were adults (aged 18 years+) in from a nationally representative sample of the English population for the time periods 2000-2003 (n=42,177) and 2004-2007 (n=36,959). METHODS Weight status was defined as body mass index (BMI) category according to WHO classification. Neighbourhood greenspace was measured using the Generalised Land use Database for England that defines greenspace as parks, open spaces and agricultural land, excluding domestic gardens. Multinomial logistic regression models were used to estimate associations between neighbourhood greenspace and BMI and, in eligible sub-samples, to investigate the contribution of total physical activity to these. All models were adjusted for age, sex, social class, economic activity, neighbourhood income deprivation and urban/rural status. RESULTS In 2000-2003 there was a counterintuitive association between greenspace and BMI. Residence in the greenest areas was significantly associated with increases in overweight (12%) and obesity (23%). In 2004-2007, there was a small protective effect of greenspace for those living in the greenest areas, but this was not statistically significant. Markers of total physical activity did not attenuate associations. Tests for interactions with urban/rural status confirmed that significant associations between neighbourhood greenspace and obesity were only present in urban areas in 2000-2003. CONCLUSIONS Better evidence for the utility of greenspace in the prevention of weight gain is required before greenspace interventions are developed.