Nest boxes for American Kestrels (Falco sparverius) may alleviate local nest site limitation, but there is concern that periodically opening nest boxes or handling adults may negatively affect nesting success. I monitored 536 kestrel breeding attempts (≥1 egg laid) in about 100 nest boxes in northwestern New Jersey, 1995–2012. To study return rates, I opportunistically captured adults in nest boxes and marked them with U.S.G.S. leg bands and patagial tags. To examine possible effects of this disturbance, I compared nesting success (≥1 nestling surviving to banding age) of marked and unmarked adults. Nesting success was 67% for 270 unmarked pairs, 76% for 25 pairs with only the male marked, 82% for 206 pairs with only the female marked, and 91% for 35 pairs with both adults marked. This significant difference likely reflects differences in the probability of capture: successful attempts last longer and successful parents may be more attentive. To control for these correlations, I examined attempts for which the first disturbance was encountering an adult in the nest box; that bird either flushed from the nest box or was captured and marked. Abandonment was not significantly related to this initial disturbance: breeding attempts continued for 94.3% of attempts in which the male flushed, 93.1% for males handled, 93.7% for females flushed, and 93.2% for females handled. Nesting success also did not differ significantly among these four treatment groups. The timing of the first disturbance did not significantly affect abandonment; breeding attempts continued for 90% of attempts in which males were first disturbed (flushed or handled) during the laying period, 94% for males during incubation, 97% for females during laying, and 93% for females during incubation. Nesting success also was not significantly related to timing of the initial disturbance. Thus, it appears that both the intensity (handling or not) and timing of disturbance had no substantial effect on abandonment or nesting success for this population.