Sirs,We read with great interest the article entitled "The effect of fluid intake on renal-length measurement in adults" by Kantarci et al. [1]. The authors have statistically made clear that the intake of oral liquid by adults shows profound increase (approximately 7%) in kidney length. Furthermore, the effect of oral-liquid intake of abnormal or diseased kidneys is unknown and needs researching [1].From this perspective, we researched whether oral hydration has an effect on kidney length between healthy children and those diagnosed with urinary tract infection (UTI). If it did have an effect, we researched whether there is a profound difference from the aspect of the increase in kidney dimension between healthy children and those diagnosed with UTI.It is known that UTI is a common bacterial infection seen in children [2] and can result in a great deal of renal pathology in the future [3,4]. For this reason, in UTI, evaluating the kidneys is crucial, and ultrasonography (US) has an important role in this matter [5]. Kidney-length measurements have a significant part in US examinations of children's kidneys and is routinely used when evaluating kidney growth over time intervals [6]. Studies carried out by De Sanctis et al. and Carrico and Zerin concerning measurement of kidney dimensions showed kidney-length measurements were much longer when measured with the patient in the supine and contralateral positions. For this reason, it is suggested that these positions should be the first preference when measuring the kidneys [7,8].By taking into consideration the points stated above, in our studies, US examinations and measurements were carried out on patients pre-and posthydration and in the supine and slightly right and left lateral decubitus positions. A total of 157 children were examined in two groups: one each of healthy (group 1) and UTI (+) (group 2) children. Group 1 consisted of 62% girls (n=57) and 38% boys (n=35), whereas group 2 consisted of 78.5% girls (n=51) and 21.4% boys (n=14). Ages in both groups varied between 4 and 11 years; the average age for group 1 was 6.9±2 and for group 2, 6.8±1.9.Results of this study are presented in Table 1. In the longitudinal dimension measurements for group 1, the average prehydration length of the right kidney was 76.5± 7.9 mm and of the left kidney 76.9±8.2 mm. In the posthydration phase, the average length of the right kidney was 81.6±8.2 mm and of the left kidney 82.1±8.5 mm. With hydration, the increase in length of the right kidney was 5.1± 1.6 mm (6.7%) and for the left 5.2±1.6 mm (6.8%). For both kidneys, length increase was statistically significant (P=0.0001 for right and P=0.0004 for the left). For group 2, however, in prehydration, the average length for the right kidney was 77.5±7.9 mm and for the left 77.8±8.2 mm. In the posthydration phase, the average length for the right kidney was 84.4±8.2 mm and for the left 84.9±8.5 mm. With hydration, the increased length for the right kidney was 6.9±2 mm (8.9%), for the left 7±2 mm (9%), and for both, the amount o...