Abstract The aim of this survey was to determine the prevalence of oral mucosa lesions in children aged 4–13 yr from two schools, one (S1) having a higher socioeconomic status than the other (S2). In all, 846 children were examined, 463 from S1 and 383 from S2, of whom 555 were boys and 291 were girls. There were 359 boys and 104 girls in S1; 196 boys and 187 girls in S2. Fifteen different lesion types were discerned. The most frequent ones were recurrent aphthous ulceration (RAU) (92 cases); fissured cheilitis (54); herpes labialis (44); angular cheilitis (30); geographic tongue (25); smooth tongue (22); and plicated tongue (17). An outstanding finding was the contrasting distribution of certain lesion types in the two schools. RAU was observed in 19% of the children from SI, making up 50% of all lesions detected. However, in S2 only 2% exhibited RAU, making up less than 4% of observed lesions. On the other hand, herpes labialis was seen in 1% of S1 and 10% of S2 children, regardless of age or sex. Plicated tongue was found in 3.2% in S1 and 0.5% in S2; fissured cheilitis in 2.9% in S1 and 12.8% in S2: and angular cheilitis in 1.1% in S1 and 6.5% in S2. Therefore, there were no statistical differences between the schools in the ratio of total lesions observed to children examined, but a significant difference was apparent when individual lesions were taken into account.