Abstract: Cognitive dysfunction is a frequently observed complication in cancer patients (Pereira, Hanson, & Bruera, 1997; Meyers & Abbruzzese, 1992; Ahles, Tope, Furstenberg, Hann, & Mills, 1996; Andrykowski, Schmitt, Gregg, Brady, & Lamb, 1992; Sjogren, Olsen, Thomsen, & Dalberg, 2000). Some research suggests that bone marrow transplantation is associated with cognitive deficits (Andrykowski, Schmitt, Brady, Lamb, & Henslee-Downey, 1992; Meyer, Weitzner, Byrne, Valentine, Champlin, & Przepiorka, 1994; Walch, Ahles, & Saykin, 1998). These studies have typically lacked baseline assessments and failed to implement standardized measures, making for weak methodology. The inclusion and comparison of both autologous and allogeneic bone marrow transplant patients is also rare. The present study was designed to provide a systematic, quantitative exploration of neuropsychological impairment in both allogeneic and autologous transplantation by employing standardized instruments prior to transplant, immediately prior to hospital discharge, and 100 days post transplant. The domains of functioning assessed included global cognitive functioning, new learning and memory, attention, visuospatial skills, language, and executive functioning. Written consent was obtained from 46 adult patients over two years. Every effort was made to assess these patients across all three time periods, however complete data was obtained from 26 patients. Statistically significant changes in functioning were revealed on measures of attention, executive functioning, memory, and language. Implications of these findings are discussed and suggestions for future research are included.