A simulation study assessed the sound levels in a Giraffe Omnibed incubator using a dummy infant and advanced sound assessment equipment. Various conditions that NICU infants might be exposed to when on a high frequency jet ventilator were simulated (incubator cooling fan and ventilator switched on or off, enclosure sides closed or open, hood up or down). The lowest sound pressure level measured was 53 decibels with all equipment off and the hood down. With all the equipment switched on the sound level was 68 decibels. Much of the noise was at low frequencies, which is difficult to reduce by conventional means. Current guidelines recommend that the sound pressure levels in a NICU should not exceed 45 decibels. NICU infants in incubators appear to be exposed to harmful sound levels.