Abstract: Abstract The pathogenicity of Paragonimus westermani with diploid form of chromosome was analysed on the basis of review of epidemiological data in Lanting of Shaoxing County from 1934 to 1982. P. westermani infected persons showed typical manifestations of paragonimiasis when the prevalence was high, while signs and symptoms turned to atypical when the prevalence was low. Whether P. westermani with diploid form would contribute to typical manifestations of paragonimiasis might be related to the frequency, number, and way of eating Sinopotamon crabs; the infection rate and intensity of Paragonimus metacercaria in the consumed crabs would also play a role in clinical manifestations.