Background: There is a growing awareness of a psychiatric construct that needs to be better defined and understood: Internet addiction (IA). Recently there has been much public concern over the relationship between Internet use and negative affect. This study explored the concept of IA and examined the relationship between addictive symptoms and depression. Sampling and Methods: An online questionnaire was used to measure participants’ Internet use, the functions for which they used the Internet, and their depressive tendencies. Three scales were included: the IA Test, the Internet Function Questionnaire and the Beck Depression Inventory (BDI). 1,319 respondents completed the questionnaires, with 18 (1.2%) identified as falling in the IA category. Results: Correlational analyses were conducted across the whole data sample. In factorial analyses, the 18 IA respondents were compared to a matched group of non-addicted (NA) respondents in terms of their scores on the Function Test and the BDI. Across the whole data sample, there was a close relationship between IA tendencies and depression, such that IA respondents were more depressed; there were also significant differences between the sexes, with men showing more addictive tendencies than women. In addition, young people were significantly more likely to show addictive symptoms than were older people. There was a significant difference between the IA and the NA group in their levels of depressive symptoms, with the NA group firmly in the non-depressed range, and the IA group in the moderately-to-severely depressed range (F1, 34 = 22.35; p < 0.001). In terms of the function for which they used the Internet, the IA group engaged significantly more than the NA group in sexually gratifying websites, gaming websites and online community/chat websites. Conclusions: The concept of IA is emerging as a construct that must be taken seriously. Moreover, it is linked to depression, such that those who regard themselves as dependent on the Internet report high levels of depressive symptoms. Those who show symptoms of IA are likely to engage proportionately more than the normal population in sites that serve as a replacement for real-life socialising. Further work needs to be done on validating this relationship. Future research is needed to corroborate the existing evidence and address the nature of the relationship between IA and depression: there is comorbidity between these conditions that needs greater investigation.