Background Older LGBT adults are growing in visibility throughout the Western world. An emerging body of research reveals that this population is at greater risk for a variety of negative physical and mental health problems compared to the general population. One such problem is loneliness, which is emerging as a major public health issue around the world. Unfortunately, loneliness has not been studied in a diverse range of older LGBT people. The purpose of this study was to assess levels of loneliness, as well as possible demographic and psychosocial predictors, in a population of older Portuguese gay men. Methods Using online surveys, 110 older Portuguese gay men (mean age = 63.5) completed the UCLA Loneliness Scale for Portuguese Older Adults, Connectedness to the LGBT Community Scale and Adjustment to Aging Scale, as well as measures of support from family and friends. Results Overall, high levels of loneliness were found, particularly among those with lower education levels. Low levels of family support, friends support and connectedness to the LGBT community were all significant predictors of loneliness in the regression analyses, but adjustment to aging was not. Conclusions These findings add to the international literature on the correlates of loneliness among older sexual minorities. Such findings may inform the development of psychosocial interventions and promote healthcare engagement among older sexual minorities, which are important steps toward reducing health disparities that affect this population.