Continuity mistake: In an early scene where the young Sally and Gillian are walking up to the aunts' house, the girls shown are the ones that play Sally's daughters and they're wearing velvet dresses. When they reach the aunts, the film shows the young girls that are actually playing young Sally and Gillian and they're wearing sailor type school girl uniforms.
Continuity mistake: Gilly is on the floor inside the circle formed by the other women to prevent her from escaping. Sally falls on her knees to be close to her sister. When the camera shows Gilly from Sally's position her head is turned right, when they are both in the shot Gilly's head is turned left
Continuity mistake: When Sally is talking to Gillian after the first failed exorcism attempt, we see Sarah is wearing white shoes; but when they are pouring the potion on the grave, she has brown sandals.