Records of children with Down syndrome (DS) at the BC Health Surveillance Registry were linked to their Birth Registrations to derive maternal ages. Incidence and maternal-age specific rates were calculated for 1952-73. Mean maternal age has declined both for normal and DS children, the latter to a marked degree, so that in 1972-73 80% were born to women under 35 years. Using maternal age of 40 and over as an indication for amniocentesis would only detect 10% of DS children. The crude incidence rate (mean 1.28/1000 livebirths) has not changed appreciably over the study period except for 1969 in which a statistically significant peak occurred. The standarized rate showed an increasing trend but it is not clear whether this was a true biological increase or resulted from better ascertainment.