Abstract: A curved ultrasonic blade including a concave top surface, a convex bottom surface and a central ridge running along the concave top surface is described. In a curved blade according to the present invention the blade has a cross section which is substantially trapezoidal. The blade edges may be sharp or blunt and the convex bottom surface has a width of at least two times the width of the central ridge and, preferably, three times the width of the central ridge. A balanced ultrasonic instrument including a curved blade having a trapezoidal cross section is also described. A balanced ultrasonic surgical instrument according to the present invention includes an ultrasonic transmission rod which is connected to the curved blade by a balance portion which includes first and second balance asymmetries designed to compensate for the imbalances induced by asymmetry of the curved blade.