The compliance with vaccination recommendations in adolescence has not been well documented in Greece. The aims of the present study were to estimate the vaccination coverage in a sample of adolescents and to identify risk factors associated with incomplete immunization. Α total of 1,005 adolescents aged 11 to 19 years who were outpatient visitors at an Adolescent Health Unit were included in this study. Participation required parental presence and consent and presentation of the official Child Health Booklet, from which immunizations were transcribed. The highest coverage rates were observed for childhood immunizations: poliomyelitis and hepatitis B (both 96%), measles/mumps/rubella (MMR; 93.1%), and meningitidis C (MenC; 83.4%). By contrast, lower rates were shown for the booster dose of tetanus/diphtheria/pertussis (39.6%), for hepatitis A (HAV; 59.1%), for the varicella vaccine (13.8% among adolescents without disease history), and among girls for the human papillomavirus vaccine (11.9%). We found a significant association between age and series completion for MMR, MenC, and HAV, with lower uptake among older adolescents . Overall, 22.7% of study participants were fully vaccinated according to criteria employed. In particular, non-urban residents, non-nationals, and females had lower likelihood of being fully vaccinated. In conclusion, our findings suggest suboptimal vaccination coverage among our sample’s adolescents, mandating that every effort should be made to increase uptake, particularly among the geographically dispersed and the culturally diverse and female adolescents.