Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder characterized by progressive muscle weakness and atrophy, often leading to severe disability or early mortality. This study aimed to estimate the prevalence of pediatric SMA in Kazakhstan and to evaluate outcomes of the national disease-modifying treatment program with nusinersen. Data from all patients registered in the national SMA registry were analyzed. SMA prevalence was calculated per 100,000 pediatric population. Survival was assessed using Kaplan-Meier analysis stratified by SMA type, and treatment outcomes were evaluated in relation to clinical characteristics and timing of therapy initiation. The national SMA prevalence was 2.9 cases per 100,000 pediatric population. Survival differed significantly across SMA types, with all recorded deaths occurring in patients with SMA type 1, while near-complete survival was observed in types 2 and 3. Kaplan-Meier analysis demonstrated a significantly reduced survival probability in SMA type 1 compared to other types (log-rank p < 0.001). Substantial delays in diagnosis and treatment initiation were observed, with a mean delay of 18 months. Earlier initiation of therapy was associated with more favorable outcomes. SMA prevalence in Kazakhstan is likely underestimated due to the absence of a national screening program. Survival outcomes vary significantly by SMA type, highlighting the importance of early diagnosis and timely treatment initiation, particularly in severe phenotypes. These findings may inform optimization of national SMA care strategies.