In patients with hepatobiliary and pancreatic cancers, surgery is the only potential curative treatment for resection candidates (Benson et al., 2009; Freelove & Walling, 2006).  A five-year research experience in patients undergoing surgery for colorectal cancer found that prehabilitation led to faster return to preoperative walking capacity than rehabilitation (Minnella et al., 2017).  There has been no studies thus far evaluating the impact of a trimodal prehabilitation program on functional recovery in patients undergoing hepatobiliary or pancreatic cancer surgery.  Our goal was to determine the impact of prehabilitation on the functional exercise capacity of these patients.  We performed a randomized controlled pilot trial comparing the impact of a prehabilitation program begun four weeks before surgery, to the same program (rehabilitation) initiated right after surgery. The program was maintained by both groups until eight weeks postoperatively. We hypothesized our prehabilitation program would improve 6-minute walk test performance preoperatively.  Furthermore, at eight weeks post-surgery, we hypothesized greater 6-minute walk performance in the prehabilitation group compared to the rehabilitation group.  Thirty-five participants were randomized to receive prehabilitation or rehabilitation. We found that preoperatively, the prehabilitation group demonstrated a clinically meaningful improvement in 6-minute walk distance.  At four-weeks after surgery, the rehabilitation group experienced a statistically and clinically significant decrease in mean 6-minute walk distance from baseline, whereas the prehabilitation group was able to maintain its baseline walking capacity.  Our findings suggest that a prehabilitation program in hepatobiliary and pancreatic cancer patients can deliver meaningful changes in pre- and postoperative functional exercise capacity.