The object of the study was to determine whether a first-morning urine specific gravity of less than or equal to 1.015 was associated with enuresis in children 3 to 6 years old. Parents of preschool children seen at the Cleveland Clinic Foundation during a 5-month period completed a questionnaire concerning bed-wetting and voiding habits of their child and collected first-morning urine specimens for specific gravity analysis. Of 101 children, 12 had a urine specific gravity of less than or equal to 1.015 (11.9%), including seven of 73 (9.6%) nonbed-wetters, two of 19 (10.5%) bed-wetters by history (who did not wet their beds on the night of the study), and three of nine (33.3%) bed-wetters (who wet their beds on the night of the study). The 73 nonbed-wetters (72.3%) had a mean (+/- standard deviation) urine specific gravity of 1.022 (+/- 0.006); 19 bed-wetters by history (18.9%) had a mean urine specific gravity of 1.024 (+/- 0.006); and nine bed-wetters (8.9%) had a mean urine specific gravity of 1.019 (+/- 0.005). The groups' mean urine specific gravities were not significantly different (p = 0.10) and the enuretic children were not more likely to have first-morning-void urine specific gravity of less than or equal to 1.015 than nonenuretic children (p = 0.14). Enuretic children who wet their beds on the night of the study had lower mean urine specific gravity than nonbed-wetters although the difference was not significant. Therefore, we do not recommend routine use of first warning void urine specific gravity analysis for predicting presence or absence of enuresis.