Patellofemoral pain syndrome—also called runner’s knee—is a common running injury characterized by pain located underneath, below, or slightly above the kneecap. The pain may be aggravated by walking or running up or down inclines, such as hills or stairs. Some people also experience an audible popping sound with movement or notice swelling in the knee area. Many runners develop this condition as a result of a large increase in training volume (e.g., mileage). Other factors include poor running form and lack of strength in the core muscles. Issues with mobility or strength imbalance in the low back and hips also may lead to the onset of patellofemoral pain syndrome. Athletes often are not aware that such issues exist until the pain starts to affect their training. Although many runners mistakenly attempt to train through the pain, this is definitely not the recommended course of action because the pain almost always gets worse. Instead, those affected by this type of pain should stop running and seek the attention of a physical therapist or other medical professional who specializes in sports injury treatment. Effective treatment of patellofemoral syndrome typically involves pinpointing and correcting the underlying cause (for example, identifying the specific area of tension and tightness and restoring mobility, flexibility, and range of motion). In some cases, gait retraining to achieve efficient running mechanics may help relieve the pain associated with patellofemoral pain syndrome.