Objective: There are no reliable markers to predict recurrence in resected Stage I non-small cell lung cancer (NSCLC). A validated clinical model to estimate the risk of recurrence would help select patients for adjuvant therapy. Methods: We reviewed the medical records of 715 patients who had a potentially curative resection for Stage I NSCLC at our institution from 1990 to 2000. Recurrence rates were estimated by the Kaplan-Meier method. A model to estimate risk of recurrence was developed by combining independent risk factors. Results: With a median follow-up of 4.7 years, the 5-year survival rates for Stages IA and IB were 66% and 55% respectively, and 5-year recurrence rates were 19% and 30%, respectively. Four factors were independently associated with tumor recurrence: tumor size > 3 cm (hazard ratio [HR] = 2.4), surgery other than lobectomy (HR = 2.0), nonsquamous histology (HR = 1.4), and high-grade cellular differentiation (HR = 1.4). A scoring system for recurrence was developed by assigning 2 points for each major risk factor (tumor size and surgery) and 1 point for each minor risk factor (histologic subtype and cellular grade). Scores were grouped as low (0 -1), intermediate (2-3), and high (>3), yielding 5-year estimates of risk of recurrence of 14%, 27%, and 43%, respectively. Conclusion: This model, based upon readily available clinicopathologic characteristics, can estimate the risk of recurrence in Stage I NSCLC, independent of T classification. This model could be used to select patients for adjuvant therapy if validated in independent data sets. © 2008 by Lippincott Williams & Wilkins.