Background Diagnostic errors contribute to the morbidity and mortality of patients. We created and utilized a novel diagnostic tool (Diagnostic Reboot) and assessed its practical efficacy in the inpatient setting for improving diagnostic outcomes. Design This was a prospective sequential controlled study that involved University Hospitalist Adult Teaching Service (UHATS) teams. Senior residents were instructed to use the Diagnostic Reboot (DxR) tool whenever a patient aged 19-99 years was identified who had an uncertain diagnosis 24 hours into their admission. Results Participating residents identified a total of 32 patients as meeting the criteria of uncertain diagnosis after at least 24 hours of hospitalization during the six months of the study period. Of these, seven were during the intervention (DxR) period. The leading diagnosis was excluded in 3/7 (43%) patients in the DxR period and 13/25 (52%) in the control period. A new leading diagnosis was made in 6/7 (86%) cases in the DxR period and in 13/25 (52%) people in the control period. A new diagnostic plan was made in 100% of the patients in the DxR group and in 80% of patients in the control group. A new consultation was requested in 4/7 (57%) patients in the DxR group and in 9/25 (36%) patients in the control group. The Residents spent an average of 20 minutes on the DxR tool. Conclusions This study demonstrated that the use of DxR may help to improve analytical thinking in residents. It may also play a role in improving outcomes in medically challenging cases, but the use of the tool during the study period was not sufficient to draw concrete conclusions. The primary barrier to the use of such a diagnostic aid was identified as time pressure on a busy hospitalist service.