This study examined the impact of using stated height instead of measured height on predicted normal values and clinical interpretation of screening spirometry in an outpatient referral population. In a prospective fashion, we evaluated 210 patients, 20 to 89 yr of age, referred for spirometry to our pulmonary function laboratory by obtaining both stated height (HTs) and measured height (HTm). The mean difference between stated and measured height progressively increased with age, from 0.80 cm (20 to 29 yr; p = 0.01) to 5.70 cm (80 to 89 yr; p < 0.001). For men and women, use of HTs instead of HTm produced a mean difference for all ages in computing predicted FEV1 and FVC values of 3.9 and 4.3%, respectively. This effect was more prominent in the older age groups (80 to 89 yr, n = 30); mean differences were 11.0% (211 ml) and 11.7% (303 ml), respectively. Use of HTs instead of HTm altered the detection of restriction by reduced FVC in 17 patients and the detection of obstruction by reduced FEV1/FVC ratio in four patients. Use of HTs altered the clinical assessment of severity by FEV1 in 15 of 108 (13.9%) obstructed patients and altered the assessment of severity by FVC in 11 of 32 (34.4%) restricted patients, with older patients more frequently affected than younger patients. We conclude that the use of stated height instead of measured height in the performance of screening spirometry can have significant impact on the calculation of predicted normal values. These discrepancies can potentially influence the clinical interpretation of screening spirometry, affecting the detection of abnormality and the assessment of severity of disease, particularly among older patients.