Congenital partial absence of the trapezius muscle is a relatively common variation. Several cases of partial absence of the trapezius muscle have been reported. However, complete unilateral agenesis of this muscle has not been previously reported. In our case, a complete cadaver dissection of an 87-year-caucasian male was performed at the Department of Anatomy, College of Medicine in Saskatoon, Canada. The entire body dissection revealed a complete agenesis of the left trapezius muscle fibers. No other significant congenital anomalies were found.