Background Maladaptive Internet use has been observed to be common among young people and particularly tertiary education students in many parts of the World outside the African continent. It has been suggested that this is on account of the fact that they form the cohort of people that are more inclined to exploit internet resources for education, communication, social interaction and entertainment. Maladaptive Internet use can simply be defined as excessive Internet use that interferes with daily life. The term has been used to describe the ‘‘overuse’’ or ‘‘abuse’’ of the Internet and its excessive or ‘misuse’ that causes problems in the users’ lives which is often accompanied by guilt, craving, and attempts to hide or reduce time online. Researchers have referred to this same phenomenon or construct by different appelations and nosologies. A growing phenomenon globally in respect of maladaptive Internet use, is its association with psychiatric disorders, notably depression. In spite of this, there is limited data on the pattern of maladaptive Internet use and its negative mental health impact among young persons in a developing country like Nigeria. Aim This study aimed to examine the pattern of Maladaptive Internet Use and its association with Depression among students of public tertiary institutions in Abeokuta, Ogun State. Methodology The study was a cross-sectional survey among the undergraduate students of the three public tertiary institutions in Abeokuta using self-administered questionnaires consisting of Socio-demographic and Internet use questionnaire, the Young Internet Addiction Test (YIAT) and the Patient Health Questionnaire-9 (PHQ-9). Data was analyzed using SPSS version 16. ii Results One thousand, one hundredand eighty-four (1184) students from the three intitutions completed the questionnaires. The mean age of respondents was 22.2 (s.d = 2.89) with most respondents (80.5%) in the age bracket of 18 – 24 years. Majority of the respondents reported that they had been using the Internet for more than four years (54.1%), used the Internet everyday (58.8%) and spent between one to six hours per week on the Internet (55.6%). One hundred and eighty nine (189) out of 1184 respondents (16.0%) met the PHQ-9 criteria for the assessment of probable depressive symptoms out of which 119 (10.1%) students were probably mildly depressed, 62 (5.2%) moderately depressed and 8 (0.7%) had probable severe depression. The prevalence rates for Maladaptive Internet Use (MIU) as defined by YIAT Scores of 50 – 100 was 36.1% (n=427) and this consisted of Borderline (Potential) Problematic Internet Use (BPIU) with score of 50-79 points and Definitive Problematic Internet Use (DPIU) with score of 80-100 points. Those with BPIU were 425 (35.9%) and those with DPIU were 2 (0.2%). Bivariate associations were observed between maladaptive Internet use and respondents’ institutions, Internet use duration, hours of use of the Internet/week, Internet use for educational purposes and probable depression. When respondents’ institutions, Internet use for educational purposes and diagnosis of probable depression were further investigated in a binary logistic regression model, all of them independently predicted MIU. Conclusion This study revealed that Maladaptive Internet use was quite prevalent among the Nigerian undergraduates in the institutions studied. The association between probable depression and Maladaptive Internet use in this study suggests the need for further studies in this direction. Tentatively, intervention strategies which should help to prevent and manage the negative impact of maladaptive Internet use among students should be encouraged. 3