Objective: To assess the natural history of congenital myopathies (CMs) due to different genotypes. Methods:Retrospective cross-sectional study based on case-note review of 125 patients affected by CM, followed at a single pediatric neuromuscular center, between 1984 and 2012.Results: Genetic characterization was achieved in 99 of 125 cases (79.2%), with RYR1 most frequently implicated (44/125). Neonatal/infantile onset was observed in 76%. At birth, 30.4% required respiratory support, and 25.2% nasogastric feeding. Twelve percent died, mainly within the first year, associated with mutations in ACTA1, MTM1, or KLHL40. All RYR1-mutated cases survived and did not require long-term ventilator support including those with severe neonatal onset; however, recessive cases were more likely to require gastrostomy insertion (p 5 0.0028) compared with dominant cases. Independent ambulation was achieved in 74.1% of all patients; 62.9% were late walkers. Among ambulant patients, 9% eventually became wheelchairdependent. Scoliosis of variable severity was reported in 40%, with 1/3 of (both ambulant and nonambulant) patients requiring surgery. Bulbar involvement was present in 46.4% and required gastrostomy placement in 28.8% (at a mean age of 2.7 years). Respiratory impairment of variable severity was a feature in 64.1%; approximately half of these patients required nocturnal noninvasive ventilation due to respiratory failure (at a mean age of 8.5 years). Conclusions:We describe the long-term outcome of a large cohort of patients with CMs. While overall course is stable, we demonstrate a wide clinical spectrum with motor deterioration in a subset of cases. Severity in the neonatal/infantile period is critical for survival, with clear genotype-phenotype correlations that may inform future counseling. Neurology ® 2015;84:28-35 GLOSSARY ACTA1 5 skeletal muscle a-actin; AD 5 autosomal dominant; AR 5 autosomal recessive; CM 5 congenital myopathy; CNM 5 centronuclear myopathy; DNIV 5 daily noninvasive ventilation; DNM2 5 dynamin 2; FTD 5 fiber type disproportion; G/J 5 gastrostomy/jejunostomy; KLHL40 5 kelch-like family member 40; MTM1 5 myotubularin; NEB 5 nebulin; NGT 5 nasogastric tube; NM 5 nemaline myopathy; NNIV 5 nocturnal noninvasive ventilation; NSMC 5 nonspecific myopathic changes; RYR1 5 ryanodine receptor type 1; SEPN1 5 selenoprotein N; TPM2 5 b-tropomyosin; TPM3 5 tropomyosin 3.