Relocation of nest sites is common among mice of the genus Peromyscus. We documented the occupation of artificial nest boxes by litters of white-footed mice (P. leucopus) at different stages of development to determine if nest relocation by lactating females is related to the developmental stage of the offspring. Three stages of development (neonates, age 0–5 d; nestlings, age 6–14 d; and juveniles, age 15–27 d) were recognized. Although the nest boxes were monitored at approximately weekly intervals, 72% of 134 litters were observed during only one of the stages of development, indicating that movement of young during lactation was common. Comparison of observed use of the boxes at different stages of development of young to expected use indicated that use of boxes was not random. Boxes were used relatively infrequently by dams with neonates and nestlings and most frequently by dams and juveniles. We believe that the suitability of a nest site to a lactating female depends on the age of her litter and that the size of the nest cavity may be an important factor in nest selection.