Intramedullary ulnar nailing may be technically difficult. We used various methods and measurements to determine the ideal nail entry point and the shape, length, diameter and curvature of the medullary canal in 44 human cadaver ulnas. We found that the ideal nail entry point was, on average, 7 mm proximal and 3 mm lateral to the most prominent area of the olecranon. A nail of 3 mm diameter could easily be inserted through a hole at the proximal-lateral side of the most prominent part of the olecranon, but only 20% of all nails could be easily inserted through a hole in the middle of the olecranon. We found that correct selection of a nail of proper length and diameter, as well as an ideal nail entry point on the olecranon are essential to successful nailing.