Background: Clinical characteristics of patients with congenital myopathies (CM) are well known but there is a lack of knowledge about the natural history and course of disease of the different genetic subtypes. In 2010 we assessed the national cohort of Danish patients with CM to decide genetic diagnosing and describe genotype- phenotype relationships. AIM of this follow-up study was to evaluate the course of disease since the initial study and to evaluate the applicability of standard assessment methods to reflect change over time and patients own opinion on the course of disease. Methods: All available genetically diagnosed patients studied by us in 2010 (n=41) were invited to the follow-up study; assessment of motor function (MFM-32), muscle strength (MRC %)and respiratory function (FVC %) and prime assessor were the same as in the initial study. Patients were asked whether the course of disease had progresses, was stable or had improved. Results: 23 patients (15-61 y) accepted the invitation. Mean follow-up time was 7.7 years. Loss of muscle strength was more prominent in patients with mutations in DNM2, RYR1 and TPM2/3 genes and deterioration in FVC % was more evident in patients carrying NEB and ACTA1 gene mutations. MFM-sum score was less sensitive to change compared to MRC-sum score. In general, agreement between the patient's own opinion of the course of disease and results of assessments was good. Conclusion: The number of patients in the study is too small to be conclusive, but the results indicate that CM can be stable or slowly progressive depending on the genetic subtype.