The aim of the present study was to investigate the efficacy of single-dose intradermal vaccination against Mycoplasma hyopneumoniae on a commercial swine unit. A total of 1051 healthy suckling piglets of 28±3 days of age were randomly assigned to one of three experimental groups: (a) intradermal: 346 piglets vaccinated intradermally (Porcilis M Hyo ID Once, Intervet SPAH), (b) intramuscular : 351 piglets vaccinated intramuscularly (Porcilis M1 Intervet SPAH) and (c) controls: 354 piglets injected with a placebo (adjuvant only). Performance parameters such as average daily weight gain (ADG), as well as health parameters and lung lesion scores were monitored from four weeks of age until slaughter. The improvement in ADG over the controls, during the finishing phase, was 27 g/day for the intradermal group and 17 g/day for the intramuscular group. Both intradermal and intramuscular vaccinations were effective in reducing clinical signs and lung lesions caused by M hyopneumoniae. Compared with the controls, approximately 10.4 per cent fewer clinical cases were diagnosed in the intradermal group, and 6 per cent fewer in the intramuscular group, during the finishing period. In conclusion, performance results were better in the vaccinated groups than in the control group, while intradermal vaccination afforded greater protection than intramuscular vaccination, especially with regard to morbidity, lung lesion and pleuritis scores.