Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 7 3 2020 12 26 154 157 EN Mahsa Alavi Namvar Department of Oral and Maxillofacial Medicine, School of Dentistry, Zanjan University of Medical Sciences, Zanjan, Iran. Sona Rafieyan Departmento of Oral and Maxillofacial Pathology, Zanjan University of Medical Sciences, Zanjan, Iran. Behzad Fathi Afkari Departmento of Oral and Maxillofacial Pathology, Zanjan University of Medical Sciences, Zanjan, Iran. 2020 09 18 2020 12 19 This article reports a 13-year-old boy with phenylketonuria and multiple superficial mucoceles on his lower lip. Phenylketonuria (PKU) is a serious and rare genetic disorder that affects the levels of amino acids such as phenylalanine in the body. If left untreated, PKU can negatively affect mental function and cause retardation. Patients with PKU receive less oral examination compared to the normal population. Mucoceles are lesions formed by the accumulation of mucous of salivary glands in soft tissue by blockage or extravasation. Local trauma has been identified as the main cause of mucoceles development. Superficial mucoceles are rare in the lower lip. These patients need close oral and maxillofacial examination to find problems, which may be related to their systemic problem. Micro-marsupialization is a conservative therapeutic approach for management of pediatric oral mucoceles. Management of trauma in patients with mental retardation is an important issue. Keywords: Mucocele; Phenylketonuria; Genetic disorder; lower lip; Salivary gland. https://jcr.tums.ac.ir/index.php/jcr/article/view/343 https://jcr.tums.ac.ir/index.php/jcr/article/download/343/304