Only 77% are being screened according to Jo's Cervical Cancer trust - and the figure drops to 72% in Belfast.
The national charity said some of the explanations women gave included confusion, embarrassment, fear and a lack of convenient appointment times.
It comes as NI's first Cervical Cancer Prevention Week is launched this week.
The campaign is aimed at increasing awareness, through advertisements on buses calling on women to take their appointments.
Cancer survivor Michelle Roe said: "If I had known that cervical screenings were to detect abnormalities before they turned cancerous, and could potentially save your life, I would never have ignored the invite that fell through my letterbox time and time again."
The first face-to-face support group for those diagnosed has also been created and the first meeting will be on 20 February in Belfast.