The odds stacked up for every successive day of the week, with the death risk from Friday surgery 44 percent higher than Monday, said a study published in the British Medical Journal (BMJ).
Lower weekend staffing levels may be to blame, according to the researchers who statistically analysed 27,582 deaths occurring within 30 days of over four million elective surgeries performed in public hospitals in England between 2008 and 2011.
"The first 48 hours after an operation are often the most critical period of care for surgery patients," said study leader Paul Aylin of Imperial College London's School of Public Health.
"As patients are operated on closer to the weekend, their immediate post-operative period overlaps with the weekend, and issues such as infections, post-operative bleeding etc. may be missed or a delay occurs in picking them up," he told AFP by email.
The weekend risk increased further for deaths within two days of an operation, to 167 percent - and this despite the fact that weekend patients generally had less risky surgery, said the team.
Only about 4.5 percent of the procedures listed were performed on a weekend.
Aylin stressed the overall risk of death from planned, non-emergency surgery was "quite low" - about 0.67 percent, but as a patient, "I would want to be reassured that the services at my hospital were running at adequate levels over the weekend period."
This is not the first study to find a higher risk from weekend surgery, but most have focused on emergency procedures.
The BMJ, in an editorial accompanying the study, asks: "Should we re-think the scheduling of elective surgery at the weekend?"
"The scheduling of elective procedures, such as knee replacements, is wholly within our control," wrote the editorial's authors Janice Kwan and Chaim Bell from the Mount Sinai Hospital and University of Toronto.
"If weekend care proves to deliver poorer outcomes than its weekday counterpart, it might be argued that elective procedures should not be scheduled at weekends at all."
Further research was needed, said the pair, into which types of procedures were affected by the so-called "weekend effect", and which patients and surgeons were best suited for weekend elective surgery.
"Until then, we are left to think twice about the adage: 'Thank goodness it's Friday'," they wrote.