To determine the long-term outcome of patients treated nonoperatively for acute or subchronic (duration of the symptoms before initiation of the treatment less than 6 months) Achilles tendinopathy, we performed a follow-up analysis on 83 of 107 patients an average 8 +/- 2 (SD) years after the initial contact. The analysis included a questionnaire, clinical examination, performance tests, muscle strength measurement, and ultrasonographic examination. Twenty-four of the 83 patients (29%) had to be operated on during the follow-up period. Seventy patients (84%) had full recovery of their activity level, and at 8 years' follow-up 78 patients (94%) were asymptomatic or had only mild pain with strenuous exercise. However, a clear side-to-side difference between the involved and the uninvolved sides was observed on the performance test, clinical examination, and ultrasonography. Also, 34 patients (41%) started to suffer from overuse symptoms in the initially uninvolved Achilles tendon. The results of our 8-year follow-up showed that the long-term prognosis of patients with acute-to-subchronic Achilles tendinopathy is favorable as determined by subjective and functional assessments. In the clinical and ultrasonographic examinations, mild-to-moderate changes were observed rather frequently in both the involved and initially uninvolved Achilles tendons, but the occurrence of these changes was not clearly related to the patients' symptoms.