The main objectives of this study were to determine the geographic distribution of low birthweight rates in London. Ontario and to identify small areas within the city that have low birthweight rates not adequately explained by the areas' socioeconomic characteristics. The following socioeconomic variables were used in a weighted, ecological, multiple regression analysis; % unwed mothers, % teen mothers, % low income, % low education, % unemployment and % immigrants. The overall variation in low birthweight rates was statistically significant and largely, but not entirely, explained by the socioeconomic characteristics of the areas. Two out of 31 census tract clusters were identified as having low birthweight rates which were higher than would be expected based on their socioeconomic profile. This methodologic approach may interest health planners as it draws attention to local factors other than socioeconomic ones which may be important when developing local strategies for low birthweight prevention.