Background Uncertainty has been studied in patients with different types of cancer, except in patients with hematologic cancer and undergoing transplantation. Objective To identify the frequency of uncertainty and its associated factors in adults scheduled to undergo hematopoietic stem cell transplantation. Methods In this cross-sectional study with analytical purposes, information on sociodemographic and clinical variables was collected. Fifty patients were diagnosed with lymphoma, myeloma, or leukemia from a high-complexity hospital. Mishel’s Scale of Uncertainty in Illness validated in Spanish was applied. A multivariate analysis was performed through logistic regression. Results Approximately 74% of participants had a high level of uncertainty. The education level (odds ratio [OR], 4.1; 95% confidence interval [CI], 1.11–15.3), family history of cancer (OR, 30.7; 95% CI, 2.7–349), and previous radiotherapy treatment (OR, 0.04; 95% CI, 0.004–0.48) were associated with the uncertainty level. Conclusions Uncertainty is experienced by patients with hematologic cancer, and factors associated should be recognized to diminish the negative effects produced by this. Implications for Practice This experience of uncertainty and its associated factors must be visible in patients scheduled to undergo transplantation. This allows nurses to carry out interventions that have an impact on the cognitive ability mediated by information and education. Reducing the effects that uncertainty has on the overall experience of patients, it is vital for nursing.