Introduction Occupational exposure to antineoplastic drugs can lead to long-term adverse effects on workers’ health. Environmental monitoring is conducted once a year, as part of a Canadian monitoring program. The objective was to describe contamination with 11 antineoplastic drugs measured on surfaces. Methods Six standardized sites in oncology pharmacy and six in outpatient clinic were sampled in each hospital. Samples were analyzed by ultra-performance liquid chromatography coupled with tandem mass spectrometry (non-platinum drugs) and by inductively coupled plasma mass spectrometry (platinum-based drugs). The limits of detection (in ng/cm2) were: 0.0006 for cyclophosphamide; 0.001 for docetaxel; 0.04 for 5-fluorouracil; 0.0004 for gemcitabine; 0.0007 for irinotecan; 0.0009 for methotrexate; 0.004 for paclitaxel, 0.009 for vinorelbine, 0.02 for doxorubicine, 0.0037 for etoposide and 0.004 for the platinum. Sub-analyses were done with a Kolmogorov-Smirnov test Results 122 Canadian hospitals participated. Cyclophosphamide (451/1412, 32% of positive samples, 90th percentile of concentration 0.0160 ng/cm2) and gemcitabine (320/1412, 23%, 0.0036 ng/cm2) were most frequently measured on surfaces. The surfaces most frequently contaminated with at least one drug were the front grille inside the biological safety cabinet (97/121, 80%) and the armrest of patient treatment chair (92/118, 78%).The distribution of cyclophosphamide concentration was higher for centers that prepared ≥ 5000 antineoplastic drug preparations/year (p < 0.0001). Conclusions This monitoring program allowed centers to benchmark their contamination with pragmatic contamination thresholds derived from the Canadian 90th percentiles. Problematic areas need corrective measures such as decontamination. The program helps to increase the workers’ awareness.