We previously reported that there is a potential for antineoplastic drug contamination throughout the hospital medication system (process flow of drug within a facility from delivery to waste disposal) due to the various surfaces contacted by health care workers. This article describes the contamination of these frequently contacted surfaces as well as identifies factors that may be associated with surface contamination. Surfaces which health care workers frequently contact were wiped and the concentration of cyclophosphamide (CP) was determined using high-performance liquid chromatography-tandem mass spectrometry. Descriptive and inferential statistical analyses were performed. A backward stepwise multiple linear regression was conducted to identify determinants associated with surface contamination. Overall, 229 surfaces were sampled, most on two occasions, for a total of 438 surface wipes. The mean CP concentration was 0.201 ng/cm(2), the geometric mean 0.019 ng/cm(2), and the geometric standard deviation 2.54, with a range of less than detection (LOD) to 26.1 ng/cm(2). (Method LOD was 0.356 ng/wipe; factoring in the surface area of the wiped surface, results in a sample LOD ranging from 0.00 to 0.049 ng/cm(2)). Our study found that frequently contacted surfaces at every stage of the hospital medication system had measureable levels of antineoplastic drug contamination. Two factors were statistically significant with respect to their association with surface contamination: (1) the stage of the hospital medication system, and (2) the number of job categories responsible for drug transport. The drug preparation stage had the highest average contamination. Those hospitals that had two or more drug transport job categories had higher levels of surface contamination. Neither the reported handling of CP prior to wipe sampling nor the cleaning of surfaces appeared to be associated with contamination.