Introduction: Swimming uses the upper extremities dominantly through strokes to create the propulsive force needed to move the body forward in the water. The consequence of continuous strokes can be the onset of pain and/or injury in the shoulder girdle, with closely related factors including shoulder strength, muscle imbalance of the rotator cuff, range of motion in the shoulder joint, and overtraining. Objectives: The main objective is to compare the muscle strength between the internal and external rotators of the upper arm in male and female swimmers. Also, an attempt is made to examine the connection between the muscle strength of the upper arm rotator and the extent of rotational movement in the shoulder joint on the dominant arm in male and female swimmers. Materials and Methods: The research included 38 male and female swimmers from Pula, born between the year 2000 and 2012. Measurements of upper arm rotator muscle strength were taken with a portable fixed dynamometer EasyForce® and the range of motion of rotation in the shoulder joint were taken with a digital goniometer EasyAngle®. The measurements were carried out at the sports facility "Gradski bazeni Dino Makovac" in Pula. Results: The T-test revealed no statistically significant difference between the muscle strength of the internal rotators and the muscle strength of the external rotators of the upper arm (P = 0.241). The muscle strength of the internal rotators (P = 0.004) and external rotators (P = 0.007) of the upper arm is statistically significant in male swimmers compared to female swimmers. There is no statistically significant relationship between the muscle strength of the rotator cuff and the range of motion of rotation in the shoulder joint on the dominant arm in male and female swimmers because the Pearson correlation coefficient according to Colton falls into the category of no relationship (from 0,00 to 0,25). Conclusion: The muscle strength of the internal rotators of the upper arm was not significantly higher than the muscle strength of the external rotators of the upper arm in male and female swimmers.