The study investigated the effect of English language use outside the classroom on written English of one hundred (100) form three students randomly selected from four secondary schools in Ilorin. Instruments used were a questionnaire, an interview, an objective test, a comprehension exercise, a cloze test and two short essays. The responses of the subjects to the questionnaire were coded into scores showing the extent and measure of their exposure to English language use outside the classroom. These were then correlated with the language proficiency measured by the tests administered. It was observed that there exists a significant mutual relationship between the degree of exposure to English language use outside the classroom and performance in written English. An exploitation of opportunities for English language activities would definitely enhance proficiency in English language.