Climate variability, such as ambient temperature, is crucial for infants' vulnerability to infectious diseases. However, little is known about how climate variability affects infectious disease mortality among infants in high mortality settings. We investigate the association between ambient temperature, seasonality and cause-specific infant mortality. Parish register data from the Sundsvall region in Northern Sweden covering the period 1868-1892 were used in combination with daily temperature data from Härnösand. Mortality due to water- and food-born diseases, airborne infectious diseases, and other causes were modelled as a function of temperature exposure in the previous 14 days using time-series analysis. We found that airborne infectious disease mortality was not related to cold temperatures but rather to seasonality, and that the summer mortality peak due to water- and foodborne infections were associated with high temperatures and not with seasonality.