The investigation will examine why the A-level student, who has worked at Bradford Royal Infirmary for the past two months, was allowed to stitch the wounds under the supervision of medical staff.
On the first occasion he was shown how to stitch a patient by a senior house officer. He then put two stitches into the woman's leg. A week later, the same woman returned with another leg wound. Watched by a staff nurse who thought he was a trainee doctor, the student put another three stitches in her leg.
Malcolm Poad, a hospital spokesman, said: "While suturing is a very minor procedure, Bradford Hospitals Trust is taking this matter very seriously ... this is an isolated incident and we are sorry that on this occasion a rare error of judgement has been made." The staff involved had been interviewed and would be disciplined.
The patient and her doctor have been contacted and given a "full explanation and apology" and similar work experience placements have been suspended pending a review.
Mr Poad said there was no possibility of such a thing happening again.
Max Madden, Labour MP for Bradford West, said: "I am very pleased to learn this scheme has been halted by the hospital trust. I will be contacting the chief executive and asking for a full explanation as to the circumstances and why this boy was offered work experience."