Five outbreaks of infectious keratoconjunctivitis (IKC) affecting alpine chamois and ibex in the western and central Swiss Alps were recorded in 2001 to 2003. Mycoplasma conjunctivae was identified from conjunctival swabs by means of a nested PCR in 27 of the 28 chamois tested. The outbreaks occurred in an area covering 1590 km2. Deep valleys acted as a barrier to the spread of the disease. A total of 409 chamois and 33 ibex with clinical signs of IKC were reported. Most of the chamois were shot, primarily because they were blind or in poor general body condition. Almost a quarter were observed alive, and 16·9 per cent died as a result of IKC. Many of the affected animals were juveniles, and more females than males died of IKC. The disease was more common during the summer and autumn. The chamois affected by IKC were found at altitudes between 550 and 3200 m. The estimated overall mortality was less than 5 per cent, but more than 20 per cent may have died locally. Ibex affected by IKC were recorded in only two outbreaks. In six places, ibex with clinical signs of IKC were found before the first affected chamois appeared in the same area.