The nematode parasite Angiostrongylus vasorum is a source of increasing concern in several parts of the world, where it causes significant disease in dogs. Wild canids, especially foxes, are likely to have a role in the epidemiology of canine infection, and the parasite could also affect fox health and population dynamics. The heart and pulmonary vasculature of 546 foxes culled mostly by gamekeepers in Great Britain in 2005–2006 were examined by dissection and a modified flushing technique. Forty foxes were found to be infected, giving an overall prevalence in the UK fox population of 7.3% (5.3–9.9). Prevalence varied widely between regions, from 0% (0–3) in Scotland and northern England to 23% (16–32) in south-east England. This closely matches the perceived incidence of disease in dogs, which is commonly diagnosed in the south-east but rarely in the north. In the Midlands, where disease has recently appeared in dogs, prevalence in foxes was 4.8% (2–11). Close geographical overlap of parasite distribution in foxes and dogs does not necessarily indicate an important wildlife reservoir of infection, but does suggest that A. vasorum might be spreading northwards. The hearts of infected foxes had thicker right ventricles than those of uninfected foxes, suggesting that the parasite could affect fox health and fitness. Burdens ranged from 1 to 59 adult nematodes. Sex, age and body condition were not significantly associated with infection. Eucoleus aerophilus and Crenosoma vulpis, nematode parasites of the respiratory system, were found in 213 and 11 foxes respectively, with slightly higher prevalence of E. aerophilus in the south and east. No specimens of the heartworm Dirofilaria immitis were found, giving an upper 95% confidence interval for prevalence of 0.84%.