Over 15 years (1983–97) 25 665 random encounter captures of adult sleepy lizards, Tiliqua rugosa, were made at a site near Mt Mary, in the mid-north of South Australia. The last months of winter (July and August) became warmer and drier in the later years of the study, and the spring months when lizard activity was highest (September and October) had increased rainfall. The lizards form monogamous pairs for an average of 8 weeks before mating in late October or early November. Pairing started earlier and lasted longer in later years of the study. The time when pairing ended showed no significant temporal trend, although it was earlier in years with warmer spring temperatures. These results suggest that the timing of reproductive behaviour was influenced by climatic variation.