OBJECTIVES. We investigated the occurrence of newly diagnosed mental retardation, attention-deficit/hyperactivity disorder, and autism and sociodemographic factors associated with their distribution in Taiwan, and we examined urbanicity- and socioeconomic status–associated differences in the age at first diagnosis.

METHODS. The data for this study were derived from the 1996–2004 National Health Insurance Research Database in Taiwan. Approximately 1.8 million beneficiaries born between 1996 and 2001 were identified, with follow-up periods ranging from 3 to 8 years.

RESULTS. Each of the 3 neurodevelopmental disorders had distinct incidence rates and associated factors. For example, as compared with the birth years of 1996–1999, the rate of autism increased 14% during the period 2000–2004, whereas the rate of newly diagnosed mental retardation decreased 42% to 50% over the same period. An elevated incidence rate for attention-deficit/hyperactivity disorder and autism was observed in later birth cohorts. The risk of receiving a diagnosis of mental retardation for children in rural areas and of lower socioeconomic status was reduced in early childhood and increased in school ages as compared with their urban and higher socioeconomic status counterparts.

CONCLUSIONS. Variation in the rate of newly diagnosed mental retardation, attention-deficit/hyperactivity disorder, and autism among children in Taiwan depended on age, birth year, period, and socioeconomic status. The extent of the association linking age with the first diagnosis of mental retardation varies across different urbanicity level and socioeconomic status.

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