Background Defaulting from scheduled appointments is common to all medical specialties but commoner in psychiatric clinics. Defaulting results in compromised quality of care, poor treatment outcomes and a drain on financial resources. In Nigeria where budgetary allocation for mental health services is poor, defaulting and its resultant consequences are burdensome. Few studies about defaulting among outpatients in psychiatric clinics in Nigeria have been reported and are lacking in the South South geopolitical zone of the country hence the need for this study. Methods A longitudinal study of a cohort of new patients attending the Out-Patient Clinics between June and December 2011 was conducted. The patients were followed up for 16 weeks to observe adherence to scheduled clinic appointments. A questionnaire was used in eliciting socio-demographic characteristics, clinical variables and patients satisfaction with treatment. Results Three hundred and ten patients were studied. A majority were aged between 26 and 35 years, with more being males (52.9%). The prevalence of missed first appointment was 32.6%. Over half (57.4%) missed second appointment and 70.0% missed the third. Patients who missed their first appointment were more likely to be single (p=<0.04) or living alone (p=<0.01) or have aggressive tendency towards property (p=0.01). Similarly, there was a significant relationship between having received previous treatment (p=<0.02), having a co-morbidity (p=<0.05) and missed first appointment. A binary logistics regression analysis showed that having previous treatment independently predicted a less likelihood to miss a first appointment. Conclusion A significant proportion of patients attending out-patient clinics at the hospital default from scheduled clinic appointments. Family and social support appears to reduce this likelihood. Additional support to caregivers, including education and other incentives may be approaches to reduce this high prevalence