Hosts, pattern of seasonal emergence and flight, and distribution of the palearctic moth Pasiphila rectangulata (L.) (Lepidoptera: Geometridae) were examined in the upper northeastern United States. Larvae developed on 29 hosts in three genera (Amelanchier, Malus, and Pyrus) in the Rosaceae. At Hamden, CT, larval density was significantly higher on ‘Delicious’ and ‘McIntosh’ apple, Malus domestica Borkhausen, than on ‘Bartlett’ pear, Pyrus communis L. Larvae were absent from ‘Napoleon’ sweet cherry, Prunus avium L.; ‘Shiro’ Japanese plum, Prunus salicina Lindley; and ‘Stanley’ European plum, Prunus domestica L., which grew in the same orchard as the infested apples and pear. In the Hamden orchard, moths were captured in emergence traps beneath apple trees over 12–15 d between late May and mid-June in 1999–2001. In 2000 and 2001, emergence was earlier for males than females, and in all years the sex ratio did not depart significantly from 1:1. Based on captures at a mercury vapor light-trap in 2000 and 2001, the adult flight lasted 1 mo between late May and late June, with the mean date of capture being statistically equal for the sexes. In 2001, more males than females were captured. The distributional range of P. rectangulata in the northeastern United States includes the New England states, extreme eastern New York, and northernmost New Jersey; specimens collected in Connecticut, New Jersey, New York, and Vermont represent new state records. The biology of univoltine P. rectangulata is similar in Europe and the northeastern United States, although the moth apparently has a broader range of larval hosts in Europe.