This paper reports the findings of a study which sought to determine whether adult ESL students with internal orientations on two dimensions of locus of control also have positive expectancies about their life situations in the United States and therefore show a higher degree of proficiency in their English interlanguage than their counterparts with external orientations on these same two dimensions. Broadly speaking, internal orientations of locus of control refer to people's belief that rewards in life are contingent on their own actions. External orientations refer to people's belief that rewards occur independently of their actions and that life situations are determined more by fate and luck (Rotter, 1966, 1975; Lefcourt, 1982). The study acknowledged that locus of control is a complex and multidimensional construct; that is, a person not only does not necessarily have similar internal or external orientations across a broad range of situations, his or her other orientations may differ with respect to the particular dimension of locus of control being measured (Wilhite, 1986). In the present study, internal-external orientations on two different dimensions of locus of control (locus of responsibility and locus of personal control) were investigated in order to observe their effect on interlanguage development. The findings show that locus of personal control correlates significantly with interlanguage development. Rationalizations for and implications of the findings are discussed.