Internet addiction is a growing addictive behavior and a major public health problem worldwide. Several psychological factors can contribute to the problematic use of the Internet. This study aimed to determine the prevalence of Internet Addiction (IA) in a sample of university students and to examine the relationship between IA, self-esteem, and attachment styles. The present study was a cross-sectional study, involving 135 students from the Faculty of Medicine of Monastir. The participants completed a questionnaire, which contained the socio-demographic data, the reasons for Internet use, the Young Cyberaddiction scale to seek IA, the Relationships-style-questionnaire-RSQ to assess attachment style, and the Rosenberg Self-Esteem Scale (RSES). The mean age of the students was 21.5 ± 1.9 years old. They were 112 (83%) females. The prevalence of Internet addiction was 23.7%. The average connection time was 3.5 ± 1.8 hours/day. The most frequent online activities were chat (online discussion, forums ...) in 94.8% of cases followed by download activities (78.5%), scientific research (75.6%), online games (23.7%), and online shopping (13.3%). IA was associated with school failure, alcohol use, online gaming, and low self-esteem. The majority of the participants (84.4%) in this study reported an insecure attachment style. Logistic regression analysis showed a strong association between IA and fearful attachment style. IA was frequent among students. Fearful attachment style was found to be a risk factor for IA. This study highlights the impact of relationships between child and their caregivers on the development of addiction.