The consequences and optimal treatment of quadriceps fibrosis following intramuscular quinine injection during childhood remain unclear. We report here a case of a 17-year-old girl who experienced unilateral quadriceps fibrosis following intramuscular injection of quinine as a baby. This case report describes the evolution of the condition during the child's growth, the long-term impact of early fibrosis on range of motion, muscle volumes, strength, gait, and activities of daily living. Rehabilitation involved orthoses and physiotherapy from the age of 6 years, when her knee flexion was reduced to 90°. A Judet quadricepsplasty was performed at 12 years because of continued loss of knee range with consequences for gait. At 16 years, knee range was satisfactory and gait variables were normalized. Functional evaluations and quality of life scales showed excellent recovery. Isometric strength of the involved quadriceps remained lower than the expected age-matched strength. Magnetic resonance imaging identified amyotrophy of the quadriceps, specifically the vastus intermedius. Despite being a focal impairment, quadriceps fibrosis had wider consequences within the involved limb, the uninvolved limb and functioning. This case report illustrates how children with quadriceps fibrosis can have a good prognosis, with excellent functional results at the end of the growth period, following early and appropriate management.