There is a paucity of research regarding aggressive behaviours of on-road cyclists and the consequences that aggression may have on their safety. To address this, we examined self-reported anger-based aggression in a sample of "active" cyclists (N = 623: males = 69%) defined as those who regularly ride a bicycle on-road (all rode at least once a week, 64% rode between 4-7 days per week). Using the Cyclist Anger Expression Inventory (CAX) three broad types of anger-based aggression were identified: 1) constructive ways of dealing with anger, 2) verbal aggression and 3) personal physical aggression. Cyclists reported that most to almost all of the time they deal with anger in adaptive constructive ways. When they were aggressive, they were most likely to express this through verbal types of aggression such as shouting or swearing aloud. Personal physical types of aggression were infrequent and these were the only type of behaviour found to be related to crashes. Regression analyses showed that factors associated with personal physical aggression included anger propensities, distance travelled, being male and younger. Interestingly, personal physical aggression was also more frequently expressed by cyclists classified as "strong and fearless" (Geller, 2009), that is avid cyclists who feel comfortable in all riding environments. Therefore, although the expressions of extreme aggression are rare, they are expressed in a group of riders who regularly ride on the road, making them particularly vulnerable. Effective strategies need to be developed to lessen cyclist aggression and mitigate the potential risks associated with these behaviours, for both cyclists and other vulnerable road users.