Caudal autotomy, the ability to shed the tail, is common in lizards as a response to attempted predation. Since Arnold's substantial review of caudal autotomy as a defence in reptiles 20 years ago, our understanding of the costs associated with tail loss has increased dramatically. In this paper, we review the incidence of caudal autotomy among lizards (Reptilia Sauria) with particular reference to questions posed by Arnold. We examine tail break frequencies and factors that determine occurrence of autotomy in natural populations (including anatomical mechanisms, predation efficiency and intensity, microhabitat preference, sex and ontogenetic differences, as well as intraspecific aggression). We also summarize the costs associated with tail loss in terms of survivorship and reproduction, focusing on potential mechanisms that influence fitness (i.e. locomotion costs, behavioural responses and metabolic costs). Finally, we examine the factors that may influence the facility with which autotomy takes place, including regeneration rate, body form and adaptive behaviour. Taking Arnold's example, we conclude with proposals for future research.