This study examines the prevalence of loneliness amongst older people in Great Britain, and makes comparisons with the findings of studies undertaken during the last five decades. In addition, the risk factors for loneliness are examined using a conceptual model of vulnerability and protective factors derived from a model of depression. Loneliness was measured using a self-rating scale, and measures of socio-demographic status and health/social resources were included. Interviews were undertaken with 999 people aged 65 or more years living in their own homes, and the sample was broadly representative of the population in 2001. Among them the prevalence of ‘severe loneliness’ was seven per cent, indicating little change over five decades. Six independent vulnerability factors for loneliness were identified: marital status, increases in loneliness over the previous decade, increases in time alone over the previous decade; elevated mental morbidity; poor current health; and poorer health in old age than expected. Advanced age and possession of post-basic education were independently protective of loneliness. From this evidence we propose that there are three loneliness pathways in later life: continuation of a long-established attribute, late-onset loneliness, and decreasing loneliness. Confirmation of the different trajectories suggests that policies and interventions should reflect the variability of loneliness in later life, for undifferentiated responses may be neither appropriate nor effective.