Multi-minicore disease (MmD) is a congenital myopathy morphologically defined by the multifocal lack of oxidative activity on light microscopy (LM) and multiple small zones of sarcomeric disorganization on electron microscopy (EM) as the main findings in muscle biopsy. We report on clinical and pathomorphological features of 17 patients diagnosed with multi-minicore myopathy at our department. Clinically, axial and proximal muscle weakness was the predominant distinguishing feature. Dysmorphic features such as high-arched palate and chest deformities were frequent findings. Limitation in cervical spine mobility was found in 4 cases. Most of our cases were slowly progressive but three fatal cases also occurred. Multifocal lack of oxidative activity was found in 16/22 biopsies on LM. Examination on EM enabled the final diagnosis of MmD in all cases. It is of special interest that in 3 patients fulfilling the criteria of pure congenital fibre type disproportion and in 2 cases of centronuclear myopathy, the findings of ultrastructural examination led us to a revised diagnosis of MmD. We postulate that all muscle biopsies with abnormal fibre proportion or centrally located nuclei as the only pathology on LM need to undergo careful EM evaluation to identify possible underlying multi-minicore disease.