Only seven cases of isolated unilateral rupture of the alar ligament had been previously reported. The authors report the first adult female case of this rare injury. The patient in their case, a 36-year-old female presented after a trauma due to falling, and at that moment, she had fainted due to a sudden pain between the neck and head. The radiological examinations [magnetic resonance imaging (MRI) and X-rays] had been interpreted as normal. She had a positive Alar ligament test at the right side, and a thin section craniovertebral junction computed tomography was obtained which revealed an asymmetrically left-sided odontoid process and a new MRI revealed a right-sided alar ligament rupture. Thus she underwent a bilateral greater occipital nerve block together with pulse radiofrequency and trigger point injection at splenius capitis, levator scapula, and trapezius followed by the application of a halo orthosis to be worn for 3 months. The patient was found to be pain-free in the follow-up examinations. With pure unilateral alar ligament rupture, the atlantooccipital joint is not disrupted and the craniovertebral junction is not destabilized. To date, only eight cases of isolated unilateral alar ligament rupture have been reported one of which was a 25 years old male; all of whom presented with marked neck pain and treated by external immobilization for 4 weeks to 4 months and our case is the first adult female patient.