Objectives: To determine fast food consumption patterns, socio-economic characteristics and other factors that influence the fast food intake of young adults from different socio-economic areas in Johannesburg, South Africa. Methods: A descriptive, cross-sectional study was undertaken, using an interviewer-administered, validated questionnaire to elicit the characteristics of the study population (adults aged from 19 to 30 years), their reasons for and frequency of fast food consumption, their specific fast food choices, and their attitudes towards health. Results: The study population (n = 341) consisted primarily of young working adults (n = 242) with at least a secondary education. Almost half (42%, n = 102) of the employed participants earned less than R5 000 per month, but spent more than R200 on fast food per month. Twenty-one per cent of all participants had fast food at least once a week, while 27.6% had it two to three times a week. Socio-economic group (SEG) and gender were significantly related to fast food intake (p < 0.01), with a larger proportion of participants (65%, n = 76) in the lower socio-economic group (LSEG) showing more frequent use. Males consumed fast food more frequently than females. The most popular fast foods consumed were burgers (69.5%), pizza (56.6%) and fried chicken (38.4%). Soft drinks were the most popular beverage consumed (56%). The main reasons for choosing fast food were time limitations (58.9%), convenience (58.2%) and taste (52.5%). The majority of the participants were concerned about their health (93.3%) and indicated a fear of becoming overweight (44.3%). Seventy-eight per cent of all the participants would have chosen a healthier option if it had been available on the menu. Television was reported to be the most effective medium influencing their food choices. Conclusion: Fast food intake appears to be very common in this group of young South African adults. Various factors that influence fast food intake were identified that provide health educators and policy makers with useful information for health promotion.