We examined how Planning, Attention, Simultaneous and Successive (PASS) processes predict reading comprehension in a sample of university students (Study 1) and what PASS processes distinguish adults with and without reading difficulties (Study 2). In Study 1, 128 university students were tested on Das-Naglieri Cognitive Assessment System, reading fluency and reading comprehension. The results of path analysis indicated that successive processing predicted reading comprehension only through the effects of text- and word-reading fluency, whereas simultaneous processing predicted reading comprehension both directly and through the effects of text-reading fluency. In Study 2, university students with (n = 20) and without (n = 23) reading difficulties were assessed on the same measures as in Study 1. The results of group comparisons indicated that the university students with reading difficulties were experiencing cognitive weaknesses primarily in successive processing. The implications of these findings for PASS theory and comprehension are discussed.