Abstract The Egyptian study of chronic hashish users comprises the largest study of psychological function in chronic users to date. It is also alone among recent studies of chronic cannabis users in suggesting impairment in psychological function as a consequence of prolonged cannabis use. Unfortunately, the Egyptian study contains several sampling and psychometric shortcomings which limit conclusions made from the study. The present paper is addressed to a critical and constructive assessment of these methodological shortcomings so that the impact of the Egyptian study can be properly evaluated. In a series of papers Soueif (1967, 1971, 1975, 1976 a, 1976 b) has presented the results of a large-scale study of chronic hashish use in Egypt. While the study examined many behavioural correlates of long-term cannabis use, including sociocultural phenomena, subjective mood effects, and attitudes towards cannabis, the focus of the present paper is the battery of psychological tests administered to cannabis users and non-users. The tests included a variety of measures assessing perceptual-motor skill (4 GATB subtests, Trail-Making Test, and Bender Gestalt), memory (Digit Span), reaction time (cards I, IV, V, and VI) from the Rorschach), and time and length estimation. Administration of these tests revealed significant differences favouring the control group on 3 GATB subtests, Trail-Making, Digit Span Backwards, and Bender Gestalt in "Copy" and "Recall" conditions. Users performed better than controls on distance and time estimation. These results led Soueif (1971; 1976 a,b) to argue for a "differential association'' of "psychological function deficits" with chronic cannabis use. The nature of these deficits, it was argued, suggested impairment in "level of cortical arousal" attributable to prolonged cannabis use. Impairment varied, however, according to the literacy, age, and residence (urban v. rural) of the user. To explain the differential association of these deficits with socio-cultural variables, 3 hypotheses were produced and apparently confirmed: The lower the level of literacy the smaller the size of the deficit; The older the S the smaller the size of the deficit; The more rural an S the smaller the impairment. The Egyptian study is quite important, if only for the reason that of several more recent cross-cultural neuropsychological studies, only the Egyptian study has produced evidence for impairment in higher adaptive cortical functions attributable to prolonged cannabis use. Studies in Jamaica (Bowman and Pihl, 1973; Knights, 1975), Greece (Dornbush and Kokkevi, 1976), and Costa Rica (Satz, Fletcher, and Sutker, 1976) have uniformly failed to show any differences between chronic cannabis users and controls of measures of higher integrative adaptive functions. The present paper is addressed to a critical and hopefully constructive assessment of the Egyptian study in an effort to reconcile these apparently discrepant studies. We hope to show that the Egyptian study, despite its size, is hampered by sampling and statistical problems of sufficient magnitude to raise questions concerning conclusions suggesting the presence of brain dysfunction. In addition, an attempt will be made to offer constructive suggestions so that the Egyptian data can be reanalysed and applied to the important question of the long-term effects of chronic cannabis use.