Object In the authors' experience, the appearance of a cervical high-intensity intramedullary (CHII) lesion on magnetic resonance (MR) images in the absence of local spinal cord compression is frequently observed in patients with achondroplasia, although it has been mentioned only sporadically in the literature. Hence, the authors conducted a retrospective study in a consecutive single-center series of patients with achondroplasia to determine the prevalence and imaging features of this entity. They also reviewed the literature. Methods Cervical MR imaging studies obtained to establish diagnoses in 25 adult patients with achondroplasia and assessed at the Leiden University Medical Center after neurogenic claudication developed were evaluated for the presence of a CHII lesion. Imaging features of the lesion were described, and a literature search was performed. The CHII lesion was demonstrated in 16 of 25 adult patients with achondroplasia (64%) in the absence of local spinal cord compression. All lesions were located at the C-2 level and appeared to be confined to the gray matter. The CHII lesion was associated with local spinal cord thinning, most likely representing focal atrophy. In their literature search the authors found no description of the CHII lesion in adults, although its presence has been mentioned as a peculiarity in the pediatric achondroplastic population. Conclusions In this large series of adults with achondroplasia and symptomatic neurogenic claudication, a CHII lesion was frequently depicted on imaging studies, but it remains a fully explored imaging phenomenon. Its cause and clinical relevance require investigation, as does its prevalence in the general achondroplastic population.