Newborn screening has dramatically reduced rates of untreated congenital hypothyroidism (CH). However, in low-income nations where newborn screening programs do not exist, untreated CH remains a significant health and societal challenge. The goal of this report is to alert health care providers about the potential of undiagnosed CH in unscreened immigrant children. We report 3 siblings of Somali descent with CH who started treatment with levothyroxine at age 0.5 years, 7.7 years, and 14.8 years and were followed for 8 years. This case series demonstrates a spectrum of severity, response to treatment, and neurocognitive and growth outcomes depending on the age at treatment initiation. Patient 1, now 22 years old, went undiagnosed for 14.8 years. On diagnosis, his height was-7.5 SDs with a very delayed bone age of-13.5 SDs. His longstanding CH was associated with empty sella syndrome, static encephalopathy, and severe musculoskeletal deformities. Even after treatment, his height (-5.2 SDs) and cognitive deficits remained the most severe of the 3 siblings. Patient 2, diagnosed at 7.7 years, had moderate CH manifestations and thus a relatively intermediate outcome after treatment. Patient 3, who had the earliest diagnosis at 0.5 years, displayed the best response, but continues to have residual global developmental delay. In conclusion, untreated CH remains an important diagnostic consideration among immigrant children.