Background Diagnosis and treatment of tendonitis/entrapment of the flexor hallucis longus (FHL) has been sporadically described in the evidence, primarily in the context of dancers and other athletes. Although various nonspecific nonoperative treatments have been described, it is not clear how often they achieve a satisfactory amount of symptom improvement. Questions/purposes The present study was designed to address the following questions regarding the nonoperative treatment of FHL tendonitis: (1) In a population of patients where the default management option for FHL tendonitis is a comprehensive nonsurgical approach, what proportion of patients thus treated opted not to have surgery? (2) What factors were associated with a patient’s decision to undergo surgery after a period of nonsurgical management? Methods The 656 patients included were all those diagnosed with FHL tendonitis who were initially treated nonoperatively in the foot and ankle division between January 2009 and December 2018. Demographics, comorbidities, examination findings, imaging results, pain scores, treatment instituted, and final outcome were obtained from the electronic medical record. The primary outcome was the decision to have surgery due to unsatisfactory symptom improvement. We compared patients who opted for surgery with those who did not after nonoperative treatment with univariable and multivariable statistics using demographics, comorbidities, and clinical findings as potential risk factors, with p < 0.05. Results Forty-four percent (180 of 409) of patients decided to forgo surgery after the institution of a specific FHL stretching program. Surgery was more likely in patients with clinical hallux rigidus (OR 2.4 [95% CI 1.16 to 4.97]; p = 0.02) or posteromedial ankle pain (OR 1.78 [95% CI 1.12 to 2.83]; p = 0.01) and less likely in those who completed an FHL stretching program (OR 0.15 [95% CI 0.08 to 0.27]; p < 0.001). Conclusion FHL tendonitis is more common than the previous evidence suggests and frequently occurs in nonathletes. Once it was diagnosed by detection of tenderness anywhere along the tendon, most frequently at the fibroosseous tunnel, nonoperative treatment focused on specific FHL stretching and immobilization in more severe cases reduced the symptoms to the extent that 44% of patients decided that surgery was unnecessary. The key to its diagnosis is awareness that this injury is possible because most patients treated in this study had been previously seen by orthopaedic providers who had not appreciated the presence of the condition, leading to a delay in diagnosis and treatment of more than a year in many patients. Level of Evidence Level III, therapeutic study.