Tilda Swinton had just given birth to twins before starring in this film, which was helpful for the film, where the display of the bodies play an important role, and her character had also just given birth.
At a public screening of this movie during the 1999 Toronto International Film Festival, one viewer was so upset and devastated that he rose to his feet and shouted that he couldn't take any more, then headed for the exit, intending to pull the fire alarm. Director Tim Roth, who was in attendance, intercepted him at the door, and it took 20 minutes of intense conversation to calm the man down.
Alexander Stuart: "Once my son was diagnosed with cancer, I had this huge amount of pain and anger about how this could happen to the child I loved so much. And I definitely directed that into The War Zone. I wrote it differently than anything I've written. I would rush back to the house while he was in chemotherapy and just write for two hours. I almost felt as if I were channeling it."
Ray Winstone and Tilda Swinton's characters are only referred to as mum and dad. This was a deliberate choice by Tim Roth so they would only be known as parents and not be referenced in any other context.