SP; classified as spastic, dyskinetic, ataxic type. The most common type is the spastic type. The ones with the best functional independence level in this group are; hemiparetic and diparetic SP. In addition to the lower extremities, the upper extremities are affected to a small extent in spastic diparetic CP. Increased lower extremity hypertonus in these children causes gait disturbances and balance problems such as fingertip, jumping, scissoring, bent knee gait. In patients with hemiparetic CP, on the other hand, hypertonus, spasticity, inadequacy in trunk control and motor losses are usually observed in one half of the body. In hemiparetic patients, the upper extremity is usually more affected than the lower extremity, and gait pathologies and balance problems are seen in different patterns. Abnormal gait patterns and balance problems are common and common problems in children with CP. As children grow, these disorders in gait become more pronounced as a result of increased hypertonus due to their taller growth. In addition, increased hypertonus and stretch reflex, muscle weakness, coactivation of antagonist muscles, posture disorders, proprioception losses, muscle and joint deformities are other factors that cause gait disorders and balance problems in these children. At this point, the main purpose of CP rehabilitation is to ensure that the child gains maximum functional independence by achieving optimal developmental potential. Therefore, balance and gait restrictions are important problems in children with CP. For these reasons, the evaluation of gait and balance is of great importance in terms of determining the effectiveness of the physiotherapy program, shaping the program, planning and determining the effectiveness of orthopedic and surgical applications, especially in children with CP who have walking potential. In the literature, gait pathologies in children with CP and easy-to-use, valid and reliable observational gait analyzes that can evaluate gait in the clinic are emphasized. These measurements are of great importance in clinical practice. Gait analysis systems including computerized kinetics and kinematics laboratories, electromyography (EMG) and video imaging are the "gold standard" methods used to evaluate the gait of children with CP. However, these evaluation methods are not routinely used in clinics because they are complex, expensive, time-consuming and not easy to apply.On the other hand, performance tests commonly used in the clinic such as the Timed Up and Go Test (TUG), the Timed Up and Down Stairs Test, the 2 Minute Walk Test, and the 6 Minute Walk Test evaluate the functionality of walking. All these tests are tests that evaluate gait prospectively and cannot fully address the child's functional status and balance problems. Therefore, in order to gain and maintain functional independence, the gait problems of the child with CP need to be examined more. In this respect, with a test such as the Modified Four-Square Step Test (mFSST), it provides a different task than normal by assessing the sustainability of postural control, which provides balance parameters by changing direction, and enables the observation of body perception, trunk stability provided by anterior-posterior cocontraction, balance, correction and protective reactions. It is performed using tape instead of canes, according to the Four Square Step test (FSST), which is frequently used in SP and found to be valid and reliable. The mFSST, a modified version of the FSST, could allow more children with CP with balance problems to complete the test while retaining the essential components of obstacle avoidance and the need for individuals to step forward, backward, and to either side. In this test, while passing over an object, the height of the object is reduced. The aim of the study is to examine the validity and reliability of the Modified Four Square Step test (mFSST) in children with CP.