The purpose of this study was to compare the efficacy of Mycoplasma hyopneumoniae vaccination with pulse medication in a pig herd chronically infected with Mycoplasma hyopneumoniae. Control groups of pigs were compared to vaccinated or treated groups. Medication and vaccination induced a significant reduction of pneumonia score (46.37% and 29.8% respectively, compared to 53.85% for control groups, p < 0.05). The treatment did not induce a significant reduction of the mean range of lung lesions (3.75) compared to the control groups (4.25). The mean range of lung lesions was significantly reduced by vaccine (3.06, p < 0.005) but not by treatment. Neither the medication nor the vaccination were able to clear M hyopneumoniae or Pasteurella multocida from lung tissue. In this herd, the vaccination had a beneficial effect on daily weight gain of pigs (695.9 g/day compared to 683.1 g/day for the control groups). The improvement of the age at slaughtering was 1.3 days for treated groups and 2.4 days for vaccinated groups compared to control groups. The vaccination induced a significant improvement in muscle rate (57.05%) compared to control groups (56.41%, p < 0.05) and to treated groups (56.21%, p < 0.001). In this herd infected with M hyopneumoniae, after allowing for treatment cost, manpower excepted, the increase in value was from -3 FF to -11 FF for the antibiotic treatment and +10.4 FF for the vaccination. From economical and medical points of view, the vaccination was preferable to the treatment under the conditions described in this study.