The aim of this paper was to examine common factors that affect condom use for sex (anal, oral and vaginal) with casual partners both known and unknown. Data were collected through in-depth interviews at one STI clinic in Stockholm, Sweden, with 29 people (14 men, 14 women and one transgendered person) aged 21-32 years participating in the study. Open questions were asked about the participant’s background, reason for STI test, reasons for condom use, reasons for condom non-use, and their definition of sex. The interviews were audio recorded and transcribed. Data were ana-lyzed according to thematic analysis. The results show that there are several reasons why people do not use a condom. Women encounter resistance from men when they suggest a condom, and often have strategies for avoiding threatening or unpleasant situations. For men, alcohol is a common reason for non-use. This is mostly connected to the effect alcohol has on their sen-sation and their erection. These findings suggest that condom use is a com-plex issue and that there are often underlying reasons why people do not use a condom. To help people be better condom users, we need to identify these underlying reasons and help patients deal with them.