Since sleep apnea is a risk factor for high mortality of rheumatoid arthritis (RA) patients, this study examined the prevalence in RA patients with occipitocervical lesions, and the associated radiographic features. Twenty-nine RA patients requiring surgery for progressive myelopathy due to occipitocervical lesions (3 males, 26 females, average age 65 years) were preoperatively evaluated. Twenty-three (79%) had sleep apnea defined as apnea-hypopnea index >5 events per hour measured by a portable monitoring device, and all of them were classified as the obstructive type. Among gender, age, bone mass index (BMI), and radiographic parameters related to occipitocervical lesions: atlantodental interval (ADI), cervical angles (O/C1, C1/2, and C2/6), and cervical lengths (O-C2 and O-C6), the ADI and cervical lengths were shown to be significantly associated with the presence of sleep apnea by parametric statistical analysis. Since there were positive correlations between the ADI and cervical lengths by Pearson's test, we performed a multivariate logistic regression analysis after adjustment for confounding factors and found that small ADI was the principle parameter associated with sleep apnea. We therefore conclude that the prevalence of sleep apnea is higher than that in a general RA population that was reported previously, and believe that occipitocervical lesions are an independent risk factor for this condition. Small ADI and short neck, secondary to the vertical translocation by RA, may cause obstructive sleep apnea, probably through mechanical or neurological collapse of the upper airway.