Background and aims: While the association between health anxiety and maladaptive Internet use is a well-established finding, no studies have been performed to examine the possible effect of abnormal illness behavior (AIB). AIB is a maladaptive manner of experiencing, evaluating, or acting in response to health and illness that is disproportionate to evident pathology. The aim of this study was to investigate the association between AIB and Internet addiction (IA) severity in a sample of Italian University students. The possible effect of alexithymia, anxiety, and depression was also taken into account. Methods: Participants were 115 men and 163 women (mean age = 23.62 +/- 4.38 years); AIB was measured via the Illness Behavior Questionnaire (IBQ), and IA severity by the Internet Addiction Test (IAT). Results: The most powerful IBQ factor predicting IA severity scores was disease conviction. Irritability was the only emotional IBQ factor associated with IA severity. Nevertheless, disease conviction and alexithymia remained the only significant predictors of IAT scores when hierarchical regression analysis was executed. Discussion and conclusions: Our results support previous findings showing that those characterized by health anxiety are more prone to an excessive and maladaptive use of Internet. Moreover, this study showed that irritability was the only emotional aspect of AIB predicting IA severity. This finding is consistent with the cognitive model of hypochondria, which states that cognitive factors (dysfunctional beliefs and assumptions) play a major role in the explanation of this psychopathological condition.