In narrow film strips, the anisotropy axis lying in the film plane and being perpendicular to the longitudinal symmetry axis of the strips, domain wall motion is influenced also by the internal stray field of the magnetic poles on their faces. This demagnetizing effect is quantitatively investigated for a simple model of a film strip containing two rigid walls. Analytical expressions for the collapse field (annihilation of a domain) and the remanent domain length are given depending on the film thickness and the strip width. Experimental tests of the domain structure by Bitter powder pattern technique are in fair agreement with the theoretical predictions.