In two studies, we compared the characteristics and retrieval times of involuntary and voluntary autobiographical memory under controlled laboratory conditions. A new laboratory task of involuntary autobiographical memories involved detecting vertical lines in a stream of stimuli with horizontal lines (an undemanding vigilance task) and recording any involuntary memories during the session. The majority of these memories were reported as being triggered by irrelevant cue phrases presented on the screen. Voluntary autobiographical memories were sampled via a standard word-cue method in Session 2. The results showed that involuntary memories were more specific and were retrieved significantly faster than voluntary memories. They were also more likely to be triggered by negative cues, whereas cue valence did not have any effect on the number of voluntary memories. Furthermore, laboratory involuntary memories did not differ from naturalistic involuntary memories recorded in a diary by the same participants (Study 2). Taken together, these results have important implications for current theories of autobiographical memory, and they open up interesting avenues for future research.