The most common etiology of non-syndromic monogenic obesity are mutations in gene for the Melanocortin-4 receptor (MC485) with variable prevalence in different countries (1.2-6.3 % of obese children). The aim of our study was 1) to search for MC4R mutations in obese children in Slovakia and compare their prevalence with other European countries, and 2) to describe the phenotype of the mutation carriers. DNA analysis by direct Sanger sequencing of the coding exons and intron/exon boundaries of the MC4R gene was performed in 268 unrelated Slovak children and adolescents with body mass index above the 97th percentile for age and sex and obesity onset up to 11 years (mean 4.3±2.8 years). Two different previously described heterozygous loss of function MC4R variants (i.e. p.Ser19Alafs*34, p.Ser127Leu) were identified in two obese probands, and one obese (p.Ser19Alafs*34), and one lean (p.Ser127Leu) adult family relatives. No loss of function variants were found in lean controls. The prevalence of loss-of-function MC4R variants in obese Slovak children was 0.7 %, what is one of the lowest frequencies in Europe.