BackgroundSeveral lesions can affect the oral and maxillofacial region, with trends influenced by lifestyle and age.AimTo investigate the occurrence of oral and maxillofacial lesions in paediatric patients assisted in an oral medicine diagnostic service in Brazil over 20 years.DesignA retrospective cross‐sectional study was performed in an oral medicine diagnostic service (1999–2019). Data included sex, age, anatomic site, and diagnosis from clinical records of children (0–9 years) and adolescents (10–19 years). Lesions were diagnosed through clinical examination. Biopsy and histopathologic examination were performed when necessary.ResultsAmong 10 530 records, 702 (6.67%) were from patients aged 0–19 years diagnosed with oral or maxillofacial lesions. A high frequency of females was observed (58.1%). Reactive/inflammatory lesions were the most common group of lesions (45.2%), followed by abnormalities of teeth/developmental defects (17.8%) and pulpal and periapical diseases (8.5%). Mucocele/ranula was the most common lesion in children (29.3%) and adolescents (25.3%). Lips were the most affected anatomic sites.ConclusionMost lesions were benign, and mucocele/ranula was the most frequent. Our results did not differ from those of histopathological‐based studies, but they provided information on the occurrence of oral and maxillofacial lesions to dentists and paediatricians.