We report our experience in a cohort of patients with hyperphenylalaninemia in a tertiary care referral center in Lebanon. Forty-one sequential patients were studied: 34 classical phenylketonuria (PKU), 3 hyperphenylalaninemia (non-PKU), and 4 biopterin metabolism defects. The majority of cases were clinically diagnosed at variable ages with variable neurological outcomes. Only 29.3% were detected by neonatal screening. Two unusual cases were observed in the context of inadequate treatment in 1 and delayed therapy in the other: a newborn with PKU developed severe keratomalacia; and a 5-year-old girl with dihydropteridine reductase deficiency due to a novel mutation identified in the quinoid dihydropteridine reductase gene developed Lennox-Gastaut syndrome and white matter changes with periventricular cysts. Part of our experience parallels that in the West. However, the clinical manifestations observed in our patients emphasize the importance of a national newborn screening program with efficient management of diagnosed cases.