Purpose The purpose of this paper is to analyse the interaction between fashion brands and consumers on social network sites. More precisely, the goal is to assess the relationship that is established between the low-cost fashion company Primark and followers of the brand on the Facebook social network in Spain, and to evaluate the brand’s use of consumer passion through this social network. Design/methodology/approach The fieldwork for this research was conducted over September-October 2015, which coincided with the final stages in the sales and the start of the autumn-winter 2015 season. The methodology was based on a daily study of all Primark publications and user interactions with the brand on Facebook. Findings The results of this study show that there is some engagement between Facebook users and Primark. However, the company does not respond to this user interaction, thereby missing opportunities in the field of consumer passion. Originality/value Until now, research into the interaction of fashion brands with users of the social networks has focused mainly on the luxury sector. This study makes an important contribution to research into the interaction between a low-cost fashion brand and users of social network sites. Primark was chosen as the focus of this case study because the brand has become a model since it broke into the mature Spanish fashion market.