To document low sound levels, the range and pattern of levels, and the relative effects of operational (staff and equipment generated) and facility (building generated) noise on the acoustic environment of a level III nursery. A quasi-experimental, prospective, longitudinal study of one bed space. Operational noise was reduced through staff behavior change while facility noise was reduced through renovation. Initial noise levels were typical of those in the literature and in recently measured nurseries. About 80% of sound levels were between 62 and 70 dBA. The lowest levels (L(min)) were 60 to 65 dBA. After staff behavior change, L(min) was about 56 dBA although the highest levels (L(max)) remained at 78 to 100 dBA. Levels following renovation were reduced to L(min)s of 47 to 51 dBA and L(max)s of 68 to 84 dBA, perceived as three or four times quieter than initially. Staff behavior as well as the acoustical characteristics of the facility determine the levels of noise and quiet in an intensive care nursery.