Abstract: Objective: The purpose of this study was to examine the levels of alexithymia in children with cancer, in siblings of children with cancer, and in healthy controls.Method: In order to compare the groups the Alexithymia Questionnaire for Children was used. The study group consisted of 97 children with cancer, 95 siblings, and 151 healthy controls.Results: The highest level of alexithymia was reported by children diagnosed with cancer, followed by their siblings. Healthy controls reported the lowest level of alexithymia. No gender differences were observed. The intensity of cancer was a significant predictor of the alexithymia score, with patients with the most severe cancers reporting the highest levels of alexithymia. No differences were found between the patients with moderately severe and least severe cancers.Conclusions: Not only children with cancer, but also their siblings show significantly more alexithymia than their healthy counterparts. Professionals should aim at preventing or reducing the psychological problems in both patients and their siblings.