This study describes the swallowing function of patients with myotonic dystrophy type 1 (DM1) and the effect of bolus consistency on swallowing in this group. The aim of the study is twofold: (a) to identify which (and to what extent) swallowing variables change for DM1 patients relative to healthy control subjects and (b) to examine whether the degree of oropharyngeal dysphagia is associated with disease severity. Forty-five consecutive DM1 patients and ten healthy subjects underwent a swallowing assessment, at Maastricht University medical Center in the Netherlands. The assessment included a standardized fiberoptic endoscopic evaluation of swallowing (FEES) protocol using different bolus consistencies. Clinical severity of the disease was assessed using the muscular impairment rating scale (MIRS). Significant differences were found between patients and controls for all FEES variables. The magnitude of these differences depended on the bolus consistency. The odds of a more pathological swallowing outcome increased significantly with higher MIRS levels. In conclusion, swallowing function is found to be significantly altered in DM1 patients. The results emphasize the importance of conducting a detailed swallowing assessment in all patients, even those with mild muscle weakness. (C) 2014 Elsevier B.V. All rights reserved.