Objective. The aim of the study was to assess the factors influencing the effectiveness of sensory integration (SI) therapy in children with sensory processing disorders (SPD). Materials and Methods. The research involved 49 children, aged 3 to 10 years, diagnosed with SPD. The study was conducted at the "Plastuś" Sensory Integration Clinics in Lodz. The research tools included acustomized questionnaire and the Sensory-Motor Questionnaire according to Z. Przyrowski. Results. The therapy showed the most significant improvement in the areas of smell (93%) and vision (69%). Progress in treatment related to muscle tension, function of the vestibular system with hyposensitivity, and coordination was affected by the examined children's age. Upon termination of SI therapy, 16% of patients showed no risk of SPD. Conclusions. SI therapy proved to be most successful in the areas of smell, vision, touch, and the hyposensitivity of the vestibular system, with the most significant correlations in progress observed between hearing, attention, and behavioral patterns. Therapy resulted in reduction in the number of areas at risk of SPD, and progress in treatment was influenced by age, the onset of walking, chronic illnesses, and the week of childbirth.