im: To assess the degree of discomfort caused by length measurement in neonates, performed with one or both lower limbs extended, on the first and second day after birth, with either one or both lower limbs extended. Methods: Healthy full-term neonates were systematically sampled during the months of February and March 2004. Crown - heel length was measured, using a 1-mm precision neonatometer, at approximately 8 h and 32 h after birth, with one and both lower limbs extended. The Neonatal Facial Coding System was used to assess discomfort during measurements. Data were analysed by parametric and non-parametric tests as appropriate. Results: Whatever the measurement technique, discomfort scores are significantly higher during the length measurement than at baseline. Whenever length measurements are performed, discomfort scores are significantly higher when extending both lower limbs rather than one lower limb (p < 0.006). The measured length is greater with one lower limb extended; however, the difference decreases over time, being 0.19 cm (95% CI 0.1-0.3; p < 0.001) at approximately 32 h of age. No significant differences in length were found between measurements at approximately 8 or 32 h, regardless of the technique used. The best correlation between length measurements with one or both lower limbs extended was observed at approximately 32 h after birth (r = 0.98). Conclusion: Measuring crown - heel length is a distressful procedure for the neonate. Measurements with one lower limb extended result in less discomfort than when both lower limbs are extended, without decreasing the accuracy.