During the 14th century AD, the inhabitants of Kutná Hora, an important urban centre in the Kingdom of Bohemia, were exposed to recurrent mortality crises. Using stable carbon and nitrogen isotopes, this study investigates the relationship between diet and the famine of 1318 and the plague outbreaks after 1346. Together with a comparative sample from regular graves, a total of 112 bone samples were collected, supplemented by 70 first permanent molars subjected to the dentine serial sampling method. The mean bone carbon isotopic value (δ13C) was − 19.3 ± 0.3‰. The mean bone nitrogen isotopic value (δ15N) was 12.0 ± 0.7‰. Individuals from famine graves showed lower δ15N values than those from regular graves. Individuals who survived into adulthood (survivors) showed higher δ15N values than those who died before adulthood i.e. non-survivors (even in the reduced sample of regular graves). Weaning age as estimated by WEAN software was 2.8 years. There was a significant difference between survivors and non-survivors but due to the smaller sample size, the confounding effect of other factors cannot be excluded. The population sample studied had a diet based on C3 plants, with a significant contribution from animal products and/or fish. Not surprisingly, those with a lower intake of animal products were more likely to die of starvation. Plague mortality does not appear to be related to dietary patterns. Apart from catastrophic events, current data suggest that a low proportion of animal products in the diet and perhaps earlier weaning reduced the chances of survival to adulthood.