Background The definition of equinus varies from less than 0° to less than 25° of dorsiflexion with the foot at 90° to the leg. Despite its pervasive nature and broad association with many lower-extremity conditions, the prevalence of ankle equinus is unclear. Furthermore, there are few data to suggest whether equinus is predominantly a bilateral finding or isolated to the affected limb only. Methods We conducted a prospective cohort study examining consecutive patients attending a single foot and ankle specialty practice. Participation involved an assessment of ankle joint range of motion by a single rater with more than 25 years of clinical experience. We defined ankle equinus as ankle joint dorsiflexion range of motion less than or equal to 0° and severe equinus as less than or equal to –5°. Patients who had previously experienced an Achilles tendon rupture, undergone posterior group lengthening (ie, Achilles tendon or gastrocnemius muscle lengthening), or had conservative or surgical treatment of equinus previously were excluded. Results Of 249 included patients, 61% were female and 79% nondiabetic. The prevalence of ankle equinus was 73% [183 of 249], and nearly all of these patients had bilateral restriction of ankle joint range of motion (prevalence of bilateral ankle equinus was 98.4% [180 of 183] among those with equinus). We also found that ankle equinus was more common in patients with diabetes, higher body mass indexes (BMIs), or overuse symptoms. Conclusions The prevalence of ankle equinus in this sample was higher than previously reported, and nearly all of these patients had bilateral involvement. These data suggest that many people attending foot/ankle specialty clinics will have ankle equinus, and select groups (diabetes, increased BMI, overuse symptoms) are increasingly likely.