Along with appearing to increase the odds for bladder cancer, prostate cancer, bone cancer, and cancer that attacks the spleen, some research suggests that neutering also appears to raise the risk in dogs for rupture of the cranial cruciate ligament (similar to the anterior cruciate ligament in a person’s knee). However, an exact cause-and-effect relationship has not been proven.
In addition, neutering raises the risk for obesity. In fact, neutering is the most commonly reported risk factor for that nutritional disorder (although a neutered dog can be kept trim with proper diet and activity).
Finally, neutering appears to increase the risk for diabetes. But whether or not that’s related to the increase in obesity is unknown.