Adequate monitoring of amphibian populations will be increasingly important if global declines are to be understood and, where possible, reversed. The natterjack toad, Bufo calamita, is the rarest British amphibian and has been the subject of substantial conservation efforts. Monitoring strategies have aimed to quantify both the total numbers of populations and the status of individual populations. Between 1970–1999 the number of natterjack populations increased from 43 to 48 because successful translocations (11) outnumbered extinctions (6). Efforts to monitor individual populations increased over the period 1970–1999. Between 1990–1999 there were no detectable trends in B. calamita population size or breeding success in Britain, although power to detect any trends over 10 years was low. Calling activity and short-term trends in spawn counts were unreliable predictors of long-term population viability in the absence of extra information such as toadlet production. Long periods (> 10 years) of spawn counts are needed to demonstrate trends that are reflective of real population changes at the national level. Efforts to develop reliable methods for monitoring B. calamita in Britain could provide useful guidelines for work on some other declining species of amphibians.