Objectives: Cricopharyngeal achalasia (CA) can be defined as inadequate opening of the cricopharyngeus muscle (CPM) resulting in dysphagia. Myosin heavy chain (MHC) isoform fiber type composition and size are key determinants of muscle function. These parameters have not been described in CA. It is hypothesized that there is a difference between the MHC isoform composition of the CPM in patients with the clinical diagnosis of CA and that in normal subjects. Methods: Patients who had received prior botulinum were excluded. The MHC fiber type composition and size in patients and cadaveric controls were determined by adenosine triphosphatase staining and image analysis. Results: The CPMs of 12 CA patients (6 male, 6 female; mean age, 61 years) and 5 control cadaveric subjects (3 male, 2 female; mean age, 67 years) were analyzed. There were relatively fewer type I fibers (67%) in patients with CA than in controls (81%), but the difference was not significant (p = 18). Type I fibers were slightly smaller in CA patients (38.7 μm) than in controls (47.2 μm), but this was not significantly different (p > 05). Of the 12 CA patients, 3 had type II predominance, a feature not seen in normal subjects. Conclusions: Patients with CA had relatively fewer type I fibers, although the difference was not statistically significant. The MHC isoform composition and fiber size were not different between CA patients and normal subjects. This is the first report to characterize the CPM in patients with CA.