This study was devoted to the formation of a spherulitic pattern in a confined space. Thin poly(methylene oxide) films, one wide and the second of width of average spherulite diameter, were crystallized isothermally at the same temperature and studied. In the narrow sample, the number of spherulites per unit area increased, whereas the length of interspherulitic boundary lines per unit area and the number of triple points, impingement points of three spherulites, per unit area were significantly smaller than in the wide sample. Computer simulation of the spherulitic crystallization demonstrated not only a decrease in the number of boundary lines and triple points per unit area due to limits of space available for the spherulitic nucleation and growth but also differences in the progression of the spherulitic structure formation between wide films and narrow strips. A model of the spherulitic pattern development in narrow strips of the polymer based on probability theory is elaborated. The model allows one to predict the rates of formation of the interspherulitic boundaries and also the distributions of distances from the spherulites centers to the boundaries for an isothermal and a nonisothermal crystallization. The total length of interspherulitic lines and the total number of triple points between spherulites can be also calculated.