Objective: The prevalence of allergic conjunctivitis (AC) has not been established. Estimates suggest that ocular allergies affect 15% to 20% of the worldwide population, yet most epidemiological studies encompass nasal and ocular allergy symptoms and have not been specific to AC. The aim of this study was to verify the prevalence of ocular allergy symptoms, co-morbidities, and their impact on adolescents. Methods: Adolescents were selected from a sample of schools, and completed in classrooms a previously validated questionnaire on symptoms of AC. AC diagnosis was considered when more than three episodes of ocular itching were reported in the past 12 months. Related symptoms such as tearing, photophobia, foreign body sensation, impact on daily activities, and diagnosis of AC were analyzed. Results: Questionnaires were obtained from 3,120 adolescents (mean age 13.3 ± 1.1 years). Ocular itching in the past 12 months occurred in 1,592 (51%). The most frequently associated symptom was tearing (74%), followed by photophobia (50.1%) and foreign body sensation (37.1%). The prevalence of AC was 20.7%, affecting more females than males (56.1% versus 45.9%; p = 0.01). The risks of an adolescent with ocular allergy to present asthma, rhinitis, and atopic eczema were (OR = 5.7; 95% CI: 4.5 to 7.1), (OR = 3.6; 95% CI: 3.0 to 4.3), and (OR = 2.6; 95% CI: 2.0 to 3.5), respectively. Severe interference in daily activities was reported by 30.5%. Conclusions: Symptoms of ocular allergy are common, frequently associated to other allergic diseases, and impact the daily activities of adolescents.