Regular physical activity (PA) is essential in cystic fibrosis (CF). This study assessed the impact of a motivational interviewing (MI)-based project titled "Just move it . . . move it," aimed at improving the PA of pediatric CF patients. At baseline and month 6, body mass index, spirometric values, and duration of extracurricular sport activities were collected. Concurrently, the maximum oxygen uptake (VO2max) was estimated. MI was performed during each visit. Overall, 19 CF children were included. Ten patients (52.7%) increased their regular PA (mean 1.9 hours/week) between both visits (PA+ group), while 9 did not (PA- group). No significant differences in functional and nutritional values were observed between the groups, while extracurricular sport time significantly increased in the PA+ group. "Just move it . . . move it" seems to be an efficient approach, as it was able to motivate several CF patients to initiate or increase their PA, yet without improving functional parameters.