Vitamin D insufficiency/rickets is a metabolic bone disease that leads to insufficient mineralization of bone. Chronic neurological diseases, including cerebral palsy (CP), convulsive disorders, neural tube defects, myopathy, immobility, lack of sun exposure, inadequate nutrition, and antiepileptic drugs (AEDs) can cause vitamin D insufficiency and osteopenia in children.In this study, the authors searched the frequency and causative factors of vitamin D insufficiency in children with chronic neurological diseases such as CP, hypoxic-ischemic encephalopathy, mental motor retardation, epilepsy, neurodegenerative and neuromuscular diseases, meningitis-encephalitis sequelae, neural tube defects, paralysis, and paresis. This cross-sectional study included 108 children (forty-five (41.6%) females; sixty-three (58.4%) males), aged between one and 18 years with chronic neurological diseases, and a control group of thirty age-matched healthy children (16 (53.3%) females; 14 (46.7%) males.Vitamin D levels were significantly lower, and parathyroid hormone (PTH) levels were significantly higher in the patient group than in the control group (p0.05), and serum Ca levels were significantly higher in ambulant patients than in non-ambulant patients (p<0.05). Vitamin D levels were significantly higher in the non-ambulant than in the ambulant patients (p<0.05). No rickets was determined in the control group, while in the patient group, nine (8.3%) had level-1 rickets, six (5.6%) had level-2 rickets, and two (1.9%) had level-3 rickets.Children with chronic neurological diseases have low serum vitamin D levels, and vitamin D prophylaxis is essential in this group.