Regression equations, based on scutal index (body length/scutal width), were developed to determine the duration of attachment for nymphal and adult female lxodes scapularis ticks. Feeding times were calculated for 444 nymphal and 300 female ticks submitted by bite victims between 1985 and 1989 in Westchester County, New York, an area where Lyme disease is highly endemic. Nymphs were attached for a mean of 34.7 hours, with 26.8% removed after 48 hours, the critical time for transmission of Borrelia burgdorferi. Attachment times increased with victim age class (Kruskal-Wallis test, p < 0.05). Mean duration of attachment for female ticks (28.7 hours) was significantly less (Kruskal-Wallis test, p < 0.05) than that for nymphs, with 23.3% attached for more than 48 hours. The 0- to 9-year age class had the highest proportion (37.1%) of females attached for more than 48 hours. Nymphs remain attached to adult tick-bite victims longer than they remain attached to children. However, children have a high risk of acquiring Lyme disease because they receive more nymphal bites and also because they are less likely to have female ticks removed in time to prevent transmission.