An environmental survey was carried out in the operating theatres of an Emilian hospital (North Italy) to ascertain: if concentrations of nitrous oxide (N2O) and isoflurane were within prescribed limits; if anesthetic pollution decreases when it is periodically controlled; if the degree of pollution from isoflurane can be predicted from N2O measurements. Three controls of anesthetic pollution were carried out at six month intervals using a photoacoustic spectrometry analyser. Mean concentrations of N2O were lower than the limits prescribed for renovated (50 ppm) or not refurbished (100 ppm) operating theatres in 58% of the surgical sessions examined. Mean concentrations of isoflurane were lower than the values proposed for halogenated anesthetics, used together with N2O (0.5 ppm) or alone (2 ppm) in 39% of the cases. Anesthetic pollution decreased only after the second control. Mean concentrations of isoflurane and N2O were correlated with a very good degree of association (r = 0.77). The survey highlights that pollution needs to be controlled in operating room because anesthetic levels often exceed the prescribed limits. Awareness of the problem is important to improve environmental conditions. N2O measurement is indicative of pollution from isoflurane but halogenated anesthetic must also be determined for a thorough evaluation of anesthetic pollution.