Objectives: Congenital hypothyroidism (CH) is still one of the most common causes of preventable cognitive impairment in children, and its early detection and treatment prevent irreversible neurodevelopmental delay. Depending on the underlying cause, cases with CH may be transient or permanent. This study aimed to compare the developmental evaluation results of transient and permanent CH patients and to reveal any differences. Methods: A total of 118 patients with CH, who were followed up jointly in pediatric endocrinology and developmental pediatrics clinics, were included. The patients' progress was evaluated per the International Guide for Monitoring Child Development (GMCD). Results: Of the cases, 52 (44.1%) were female, and 66 (55.9%) were male. While 20 (16.9%) cases were diagnosed with permanent CH, 98 (83.1%) were diagnosed with transient CH. According to the results of the developmental evaluation made with GMCD, the development of 101 (85.6%) children was compatible with their age, while 17 (14.4%) children had delays in at least one developmental area. All 17 patients had a delay in expressive language. Developmental delay was detected in 13 (13.3%) of those with transient CH and 4 (20%) with permanent CH. Conclusions: There is difficulty in expressive language in all cases of CH with developmental delay. No significant difference was found between the developmental evaluations of permanent and transient CH cases. The results revealed the importance of developmental follow-up, early diagnosis and interventions in those children. GMCD is thought to be an important guide to help monitoring the development of patients with CH.