The ability to accurately estimate changes in muscle cross-sectional area (CSA) could be a useful tool for strength and conditioning practitioners to assess the effectiveness of a resistance training program. The purpose of this study was twofold: (a) to compare the reliability of 2 separate anthropometric-based field estimations of thigh muscle CSA with that of a more accurate, sophisticated imaging technique (peripheral quantitative computed tomography [pQCT] scanner) and (b) to determine if the field methods would be sensitive enough to detect changes in CSA during a resistance training program. Twenty-five healthy, untrained men completed 8 weeks of resistance training. Cross-sectional area testing occurred twice before the start of training, for reliability and again every 2 weeks during the study. Testing consisted of a pQCT scan of the right thigh followed by circumference and skinfold measurements. Two separate equations (Moritani and deVries [M + D] and Housh multiple regression [HMR]) were used to estimate CSA from the anthropometric data. The M + D and HMR methods demonstrated intraclass correlations of 0.983 and 0.961, respectively, but both significantly underestimated thigh muscle CSA when compared to the pQCT. This error was consistent, however, and consequently, the field methods were able to demonstrate increases in muscle CSA with a pattern similar to those from the pQCT. Thus, these equations can be useful tools to evaluate an athlete's progress toward the goal of increasing muscle CSA. It is the authors' hope that the present study will increase awareness among practitioners of these useful field methods for estimating training-induced changes in muscle CSA.