Lujan-Fryns Syndrome (LFS) is defined as a set of symptoms including mild-moderate mental retardation, marfanoid appearance, hypotonia at birth, hypernasal speech, characteristic craniofacial appearance and normal testis size. The frequency of the syndrome is not known thus the information obtained is solely based on case reports. Hereby, we present a patient with LFS diagnosis. The 29-year old male patient had mental retardation, aggression, and persecutory delusions, characteristic craniofacial and marfanoid features. During his speech pronominal reversal was observed ('the hurt him, he is so upset' when talking abour himself). After examination and genetic analysis, fragile X, Klinefelter, Marfan and Down syndromes and homocystinuria were eliminated as causes of mental retardation. A preliminary diagnoses of LFS done. No mutation was detected in exon 22 of the MED12 gene; but. Whole Exome Sequencing (WES) is ongoing. The patient was started on risperidone (4 mg/day) for psychotic symptoms and carbamazepine (200 mg/day) for impulse control and as an antiepileptic. After a follow up of 8 months, impulse control, psychotic symptoms and aggression improved significantly. Since the specific gene mutation of LFS was not determined in our case, we solely had to depend on clinical evaluation and genetic analysis. Although it is not easy to fully define or classify these syndromes, we believe every reported case will be a step in overcoming these difficulties.