Aims: To identify the incidence of allergic conjunctivitis in patients with allergic rhinitis. Methods: One hundred and eighty seven consecutive patients with allergic rhinitis (AR) were directly questioned if they have allergic conjunctivitis (AC) and this was clarified using standard screening questions relating to red, itchy and watery eyes recorded through a total ocular symptom score (TOSS). Patients were also asked about further symptoms that may be attributable to AC: eyelid dermatitis, frequent blinking; eye sensitivity and frontal headache from squinting or. blinking. All patients were given a drop of olopatadine hydrochloride 0.1% in each eye to help identify "silent" disease. 20 healthy non-atopic controls were also treated with olopatadine drops and questioned on ocular symptoms. Results: Fifty five percent of patients with AR were identified as having AC by direct questioning and the use of the TOSS questionaire. A further 41% were identifiable by asking additional questions and performing therapeutic challenge with olopadatine. Conclusions: AC is a frequent comorbid condition occurring in 95% of our patients with AR. Only 55% of patients were able to identify that they had AC based on standard screening questions. Additional specific questioning and a therapeutic challenge in suspected patients can help identify patients who may benefit from treatment of AC.