Background: Limited studies exist on the factors associated with a complete cure of onychomycosis in older adults.Objectives: To determine the age and factors associated with a complete cure among older adults diagnosed with toenail onychomycosis.Methods: A retrospective cohort study was conducted of 95 older adult patients (aged ≥ 60 years) diagnosed with toenail onychomycosis between January 2016 and December 2017. Demographic data, mycological findings, treatments and durations to a complete cure were reviewed.Results: The complete cure rates of the patients aged < 70 years and ≥70 years were 67.4% and 44.9%, respectively (P = 0.027). Patients aged ≥ 70 years were significantly higher in male gender, had higher history of smoking, peripheral arterial disease, impaired renal function, antihypertensive drug and amorolfine nail lacquer usage, and polypharmacy. A multivariate analysis revealed that being aged ≥70 years and having a nail thickness >2 mm were associated with failure to achieve a complete cure. The median times to a complete cure for older adults aged <70 years and ≥70 years were 20 months and 47 months, respectively (P = 0.007).Conclusions: An age ≥ 70 years was related to a lower cure rate and delays in achieving a complete cure. A nail thickness > 2 mm was a poor prognostic factor for a complete cure. Moreover, very old adults were more likely to suffer side effects arising from the use of systemic antifungal medications.