Purpose The 20-year survival rates are unknown for the majority of melanoma patients—those with thin melanomas. We determined 20-year survival rates of patients diagnosed with thin melanomas (≤ 1.00 mm) in the general population and also determined the main prognostic factors. Patients and Methods Available clinical and histologic data from the Queensland Cancer Registry were obtained for all patients diagnosed with a single thin invasive melanoma from 1982 to 2006 and matched against national death registration data. Melanoma-specific survival estimates to December 31, 2007, were assessed, and subgroup differences in prognosis were determined by fitting multivariate Cox proportional hazard models. Results Among 26,736 people in the state of Queensland diagnosed with thin melanomas, the 20-year survival was 96%. The most influential determinants of prognosis were tumor thickness ≥ 0.75 mm (adjusted hazard ratio [HR], 4.33; 95% CI, 2.8 to 6.8 compared with tumors < 0.25 mm) and patient age at diagnosis older than 65 years (HR, 2.8; 95% CI, 1.8 to 4.5) compared with age younger than 25 years. Acral lentiginous and nodular tumors, male sex, tumor site on the scalp or neck, or tumor invasion of the entire papillary dermis each independently increased the risk of dying from thin invasive melanoma. Conclusion The outlook for patients with thin invasive melanoma is positive, although continued clinical vigilance is warranted for patients with nodular melanoma and those with the thickest tumors.