Intersucking is an abnormal behaviour in dairy heifers and cows, and it is defined by one animal sucking the teat of another animal with the intention of sucking milk. The aim of this paper is to review earlier studies on intersucking in dairy cattle and to present results from a questionnaire about intersucking in Swedish cattle. In previous studies 1–49% of the dairy farmers have reported intersucking in cows, and 0.5–40% of the cows have been observed intersucking. Many factors have been found to be related to the development of intersucking, for example, the milk feeding method and housing of calves, the feeding methods of heifers, and the feeding and housing of cows. There also seems to be a relation between cross-sucking in calves and intersucking in heifers and cows. It has been claimed that intersucking between heifers leads to mastitis in primiparous cows, and especially the Corynebacterium pyogenes mastitis. A large number of preventive measures have been tested to stop intersucking in cows, but with varying success. A questionnaire was answered by telephone interviews to 230 dairy farms in Sweden with a reply frequency of 66%. Intersucking had been observed between cows on 29.4% of the farms, and between heifers on 60% of the farms. Calves had been observed sucking under the belly of other calves on 60% of the farms. There was a significant relationship between observations of calves sucking under the belly (cross-sucking) and heifers intersucking ( P<0.001), and between observations of intersucking in heifers and intersucking in cows ( P<0.05). In calves, out of 17 different housing, milk feeding and management factors tested, only 3 turned out to be of significant importance in relation to sucking under the belly. These were: kept in groups and given milk in open buckets ( P<0.0001); kept in groups and given milk by computer controlled feeders ( P<0.05); given more than 6 l of milk per day ( P<0.05). In heifers, out of 15 different factors tested, only 2 turned out to be of significance in relation to intersucking. These were: receiving a concentrate:roughage (C:R) ratio lower than 30:70 ( P<0.05) and pregnant heifers being housed with cows ( P<0.05). In cows, the only factor that turned out to be of significance in relation to the occurrence of intersucking was loose housing ( P<0.01, 40.2% loose housed and 21.5% housed in tether stalls). The occurrence of intersucking in heifers was a risk factor for reports of C. pyogenes mastitis in heifers ( P<0.01). The farmers’ method to stop intersucking in both heifers and cows was to place a bull ring or anti-self milker on the muzzle of the intersucker, to house them in tether stalls or to re-group the heifers or, if this failed, to cull the intersucking individual. It is concluded that intersucking occurs on a relatively large number of dairy farms, but only in few individual cows and more commonly in heifers and calves (as cross-sucking). Since the problem behaviour starts early in life, actions should be taken to improve the milk feeding methods of calves and management of replacement heifers.