Northern Harrier (Circus cyaneus) nest success was studied in relation to habitat choices and availability from 1980 to 1982 in New Brunswick. Measurements of moisture, vegetation, and visibility at nest sites indicated that harriers most often used wet sites surrounded by cattails, with high visibility. Moisture and vegetation had a significant effect on nest success (p < 0.03), while visibility played no significant role. Discriminant analysis indicated that of the three variables, moisture was consistently the best predictor of nest success over 3 years (≥ 64%). Paradoxically, the order of settling by females was weakly correlated with the quality of nest sites in these years, yet choice was not limited by availability. We suggest, therefore, that nest site selection was a compromise between a wet nest site, close proximity to optimum foraging habitat, and, for females, access to a mate with a high food provisioning rate.