Breeding of the threatened long-tailed bat Chalinolobus tuberculatus was studied over seven summers, 1993–2000, in temperate rainforest, Fiordland, New Zealand. Reproductive history of 789 marked bats from three social groups was investigated. Seventy per cent of births occurred over a 10-day period in mid-December. Young began flying at 5–6 weeks and nipples of reproductive females were regressing 2 weeks later. Sex ratio at birth was equal. Lactation coincided with highest annual air temperatures and peak abundance of flying invertebrates. Date of first birth varied by 4 days annually, but date of first flight varied by 17 days. Males had distended cauda epididymides at 1 year old (mean±SE = 1.63±0.16 years) and epididymal distension peaked in early autumn. Females first gave birth at 2–3 years of age (2.33±0.08 years). The short, highly synchronous breeding season, birth of single young, early mating in autumn, and late age of female sexual maturity compared to similar-sized vespertilionids, may be related to low food availability and unpredictable cold-temperate weather conditions. Annual productivity did not differ among groups but probability of survival of juveniles varied from 0.26 to 0.88 and was inversely proportional to size of natal group. Variability in breeding parameters was unrelated to climate or body condition of bats. The group with highest survival rates contained reproductive females and juveniles with significantly higher body condition. Differences in roost site or food quality within the home range of each group, varying genetic quality of members of the groups, or density-dependent mechanisms, may explain differential survival, but these hypotheses require investigation. A population crash and poor productivity in 1996 coincided with an irruption in the numbers of stoats Mustela erminea implying that predation by introduced animals can cause periodic population crashes. These results should be used to examine implications of these hypotheses on the long-term viability of Chalinolobus populations.