Noise in neonatal intensive care units (NICUs) may impede growth and development for extremely low-birth-weight (ELBW, < 1000 g) newborns. We calculated correlations between NICU sound levels and ELBW neonates' heart rate and arterial blood pressure to evaluate whether this population experiences noise-induced stress. Sound levels inside the incubator, heart rate (HR), and arterial blood pressure recordings were simultaneously collected for eight ELBW neonates for 15 minutes during the first week of life. Cross-correlation functions were calculated for NICU noise, HR, and mean arterial blood pressure (MABP) recordings for each subject. ELBW neonates' HR and MABP were significantly correlated ( R = 0.16 at 2-second lag time), with stronger correlation apparent for higher-birth-weight ELBW newborns (0.22 versus 0.10). Lower-birth-weight newborns responded to increased noise with HR acceleration from 45 to 130 seconds after noise events, and higher-birth-weight infants initially responded with an HR deceleration at 25 to 60 seconds, then HR acceleration ~175 seconds after noise increased. MABP was not as strongly correlated with NICU sound levels, although some correlation coefficients were slightly outside the 95% confidence interval. Higher-birth-weight newborns' more mature neurological systems may be responsible for stronger correlations between HR and MABP. NICU noise influenced newborns' HR, indicating that these infants hear and respond to NICU sounds. ELBW newborns in the first week of life seem to maintain a relatively stable blood pressure in response to moderate NICU sound levels (50 to 60 dBA).