This study was undertaken to determine how prior knowledge of BASIC computer language affects the achievement in introductory computer science courses at university. It looked at comparisons of achievement in introductory computer science courses at the University of British Columbia (U.B.C.) among groups who have learned BASIC, or who have learned other languages, or who have learned no languages. It investigated comparisons of achievement among demographic factors: gender, age, Faculty, and major. Achievement differences in first year FORTRAN courses, in first year Pascal courses and in a second year Pascal course, among groups of students with different backgrounds were also examined. The study investigated the effect on achievement of "how well", "when", and "where" either BASIC or Pascal had been learned. Finally, it identified factors that are the best predictors of success in introductory computer science. A questionnaire was distributed in six introductory computer courses at U.B.C. during the school year 1985-1986. Marks were collected in these courses at the end of the year. After matching by student number a sample of 1194 students was analyzed using the analysis of covariance and the multiple linear regression routines of the Statistical Package for the Social Sciences (SPSS). It was found that students who have taken BASIC language do better in university introductory level computer science courses than those who have no prior knowledge of a computer language, and they do as well as those who have prior knowledge of some other computer language. It was discovered that students who have previously learned a computer language have better achievement than those who have not learned a language. Students with a knowledge of at least two languages have an even higher achievement. The order of learning BASIC language was observed not to be significant in subsequent computer science achievement. Males had higher achievement than females in the surveyed courses. The younger students tended to have higher achievement than the older students in these courses. Achievement differences were found among the Faculties involved. Students who were majoring in mathematics outperformed those who were non-mathematics majors within the Faculty of Arts. Achievement in the second year course did not appear to be dependent upon the computer language background prior to entering university. Students who were able to write complex BASIC programs outperformed others with a limited familiarity with BASIC language in introductory computer science courses. For students who had prior knowledge of Pascal language the level of how well the language had been learned did not appear to be a factor in introductory computer science achievement. The age at which BASIC or Pascal language was first learned was a critical factor. Those who first learned the language in the 13 to 18 age range outperformed others who first learned the language at an older age. The place where either BASIC or Pascal language had been learned did not appear to be a critical factor for achievement in introductory computer science. Only the overall year percent in all other courses taken and the variable as to "how well" BASIC language had been learned, proved to be significant factors in predicting success in introductory computer science. The writer concludes that the results of this study provide sufficient evidence to support the argument that BASIC language should continue being taught in pre-university computer science courses.