This research tested the hypothesis that learners whose exposure to a second language begins before the age of 15 years achieve higher syntactic proficiency in the target language than adult learners. Sixty-seven immigrants who had come to the United States at various ages and who had resided in this country for various periods of time were tested for syntactic proficiency in English and were also administered a questionnaire to gather information concerning practice and instructional variables. Age at arrival was found to be a strong predictor of syntactic proficiency while other independent variables had very little effect. The results were interpreted as providing support for the hypothesis of an age related limitation on the ability to acquire full command of syntax in a second language.