Introduction: Visible changes in self-concept among pediatric patients with cancer are a bothersome experience that may accompany them until adulthood. Purpose: To explore the self-concept and in particular the physical appearance and popularity in children with cancer compared to healthy ones. Methods and material: A descriptive correlational study of 100 children (50 healthy and 50 diagnosed with different forms of cancer) ages 8 to 10 years. Participants were recruited from a public hospital in Athens Greece. The research instrument was “Piers-Harris Children’s Self-Concept scale” which included patients’ characteristics. The data were analyzed with the SPSS-12 statistical packet by using the following statistical tests: χ2-test, nonparametric Mann-Whitney U-test, Kruskal-Wallis test. Results: It was found that children with cancer reported more negatively or both physical appearance and popularity (p ≤ 0.001) compared to the healthy ones. Moreover, the 8-year-old children with cancer reported more negatively for physical appearance (p ≤ 0.001) but not for the factor popularity (p = 0.021), while the 10-year-old children with cancer present a more negative body image relative to the healthy ones, only for the factor popularity (p ≤ 0.001) but not for the factor physical appearance (p = 0.134). In terms of gender, female subjects with cancer presented a more negative body image relative to the healthy female subjects for both factors examined (p ≤ 0.001), while male subjects with cancer presented a more negative body image relative to the healthy male subjects only for the factor physical appearance. A positive correlation between popularity and physical appearance was found (p ≤ 0.001) but only among the children with cancer. Conclusions: The present results highlight the differences in physical appearance and popularity among children with cancer and their healthy counterparts. The recognition of the role of physical appearance as a significant factor for children with cancer may inform the development of effective interventions for this group of children.