Large carnivores inspire opposition to conservation efforts owing to their impact on livestock and human safety. Here we analyse the pattern of lion attacks over the past 15 years on humans in Tanzania, which has the largest population of lions in Africa, and find that they have killed more than 563 Tanzanians since 1990 and injured at least 308. Attacks have increased dramatically during this time: they peak at harvest time each year and are most frequent in areas with few prey apart from bush pigs (Potamochoerus larvatus), the most common nocturnal crop pest. Our findings provide an important starting point for devising strategies to reduce the risk to rural Tanzanians of lion attacks.