Atlantoaxial subluxation due to minor trauma manifesting with progressive quadriplegia is rare. We present a case in a 38-year-old man who had ankylosing spondylitis for 10 years. The patient initially had right arm weakness, which progressed to bilateral upper and lower extremity weakness within one month. Ten days prior to referral to the emergency department (ED), lie fell and was totally bed-ridden with quadriplegia. Two-dimensional computed tomographic (CT) scan of the C- spine performed in the ED demonstrated atlantoaxial subluxation. Conservative supportive treatment was suggested and he was discharged in stable condition 46 days later.