Impedance monitoring (IM) of cardiorespiratory (CR) function is commonly used in the intensive care units and the general pediatrics ward, as well as in the home. Location of the leads on the thorax is particularly important in infants who have a compliant chest wall (Pediatr Pulmonol 1992;12:247). To determine whether the location of lead placement also affects the quality of data obtained during IM of older children and adults, we monitored CR function in 45 patients using a recording IM (Model 511, Corometrics, Wallingford, CT) simultaneously with the first four hours of full overnight polysomnography(PSG) in a sleep laboratory. The PSG included staging of sleep, nasal and oral airflow, effort assessed by respiratory inductance plethysmography, and oxyhemoglobin saturation. All PSG data were scored by one of the investigators(LJB) without knowledge of the impedance data. The patients ranged in age from two to 74 years; 28 were male and 17 were female. Twenty-two patients had their impedance leads placed high on the chest (second to third intercostal space (ICS), midclavicular line (MCL)), three had low lead placement (ninth to tenth ICS) and 18 had an intermediate lead placement. Two patients had diagonal lead placement (fifth to sixth ICS, right MCL, second to third ICS, left MCL). Five of 22 patients (23%) with high lead placement required a change in electrode position because the technician judged the impedance signal to be unsatisfactory; all other positions resulted in a visually satisfactory signal (p<.05). IM identified 185 respiratory events; 100 of these (54%) were confirmed on PSG. High lead placement resulted in a significantly higher proportion of false alarms than did any other position(p<.001). There was no effect of age, gender, or body mass index on the percent of false alarms. There were no central respiratory events recorded on PSG that were not recorded on IM. We conclude that proper lead placement for IM is important in minimizing false alarms in older children and adults as well as in infants, and the best signal quality is obtained by placing the electrodes on the mid to lower portion of the chest. Funded by Corometrics Medical Systems.