Objective:The aim of this study was to estimate population based incidence rates for infantile spasms (IS) and to study our clinical impression that the incidence of IS has recently decreased in the Canadian Provinces of Nova Scotia and Prince Edward Island.Methods:Birth cohorts from 1978 to 1998, identified through the hospital health records, EEG records and physician computerized databases, were followed for two years for the development of IS. Disease incidence rates were calculated using denominators derived from Statistics Canada's reported annual live birth rates.Results:The inclusion criteria for IS were fulfilled by 75 patients. The overall incidence of IS was 30.7/100,000 live births (95% CI 24.3, 38.8). Etiologic classification was symptomatic for 51 cases (68%), cryptogenic for 18 (24%), and idiopathic in six children (8%). Although there were more males (N=44) than females (N=31), the incidence rates were similar. There was a marked variability in annual and five-year incidence rates.Conclusion:Although the clinical characteristics of our patients were similar to other reported IS populations, the instability in IS incidence rates indicates a need for caution in interpreting smaller IS epidemiologic studies.