Psoas syndrome is an easily missed diagnosis. However, it is important to consider this condition as part of the differential diagnosis for patients presenting with low back pain—particularly for osteopathic physicians, because patients may view these practitioners as experts in musculoskeletal conditions. The authors describe the case of a 48-year-old man with a 6-month history of low back pain that had been attributed to “weak core muscles.” The diagnosis of psoas syndrome was initially overlooked in this patient. After the correct diagnosis was made, he was treated by an osteopathic physician using osteopathic manipulative treatment, in conjunction with at-home stretches between office treatments. At his 1-month follow-up appointment, he demonstrated continued improvement of symptoms and a desire for further osteopathic manipulative treatment.