The primary and proven therapy, in cases of celiac disease (CD), is a rigorous gluten-free diet. However, there are reports of its negative effects in the form of nutritional deficiencies, obesity and adverse changes in body composition. The aim of the study was to assess the impact of a gluten free diet (GFD) on the body composition of children with CD. In a case-controlled study (n = 41; mean age 10.81 y; SD = 3.96) children with CD, in various stages of treatment, underwent medical assessment. The control group consisted of healthy children and adolescents, strictly matched for gender and age in a 1:1 case-control manner. More than half of the examined children (n = 26) followed a GFD. CD children had significantly higher mean values of the fat free mass (FFM% = 80.68 vs. 76.66, p = 0.015), and total body water (TBW% = 65.22 vs. 60.47, p = 0.012), and lower mean values of the fat mass (FM% = 19.32 vs. 23.34, p = 0.015). Children who were on a GFD presented slightly higher, but not statistically significant, mean values of FM and FFM, than children who did not follow dietary recommendations (FM [kg] = 7.48 vs. 5.24, p = 0.064; FM% = 20.81 vs. 16.73, p = 0.087; FFM [kg] = 28.19 vs. 22.62, p = 0.110). After minimum one year of a GFD, CD children showed significantly higher values of FFM [kg] (p = 0.001), MM [kg] (p < 0.001), TBW [L] (p < 0.001) and BCM [kg] (p < 0.001). Furthermore, CD children who were on a GFD presented significantly higher weight (p = 0.034) and body mass index (BMI) (p = 0.021) increase. The children adhering to a GFD demonstrate a tendency towards higher indices of selected body composition components.