Extreme birth weights are associated with increased infant mortality and morbidity. Identifying infants of extreme birth weight is important for both clinical assessment and public health research. This study aimed to produce charts of birth-weight percentiles by gestational age for male and female, black and white infants in Connecticut. Data were obtained from registrations of live births to Connecticut residents in Connecticut, 1988-1993. During this period 263,032 births were registered to black and white women. Birth weight was missing in only 90 records but gestational age was missing in 29,865 (11%) records. An additional 0.5% of births were excluded because the recorded birth weight was an extreme outlier for the recorded gestational age. Birth records with missing gestational age had lower mean birth weights and proportionately more births < or = 1500 g when compared to birth records where gestation was reported; however the magnitude of the differences was small. Our charts provide population-based birth-weight percentiles by gestational age based on the most recent Connecticut birth data available. They are the most appropriate population norms available for Connecticut clinicians and researchers.