Mucocutaneous disorders in children with Down syndrome: case controlled study: Objective: Down's syndrome is the most frequent chromosomal anomaly that can affect a multiple organ systems, including skin. In this study, we compared the frequency of mucocutaneous disorders in children with Down's syndrome with normal children. Methods: We recruited fifty children with Down's syndrome and 50 healthy children as a control in our study. Mucocutaneous abnormalities were examined in both groups. Findings: Of 50 patients, 22 were girls and 28 were boys. The skin findings such as xerosis and Mongolian spots were the most frequently seen in the patients with Down's syndrome. Seborrheic dermatitis, cheilitis and fissured tongue were seen frequently, as well. The rare findings were plantar hyperkeratosis, alopecia areata, geographic tongue, cafe-au-lait macula, livedo reticularis, cutaneous infections, pityriasis capitis simplex, cutis marmorata, neurotic excoriation, trichotillomania, keratosis pilaris and diaper dermatitis. No mucocutaneous finding was seen in 16 patients. The prevalence of the skin disorders including Mongolian spot, seborrheic dermatitis, cheilitis, fissured tongue was significantly higher in patients with Down syndrome than normal individuals (p<0.05). Conclusion: Therefore, large-scaled epidemiological studies covering the entire population are needed. We believe that these studies could provide better understanding the dermatological diseases in children with Down's syndrome that would help to practitioners to treat these problems.