Abstract Objectives Fibrodysplasia ossificans progressiva (FOP) is an ultra-rare genetic disorder characterized byheterotopic ossification (HO) and progressive restriction of mobility. To date, no approved disease-modifying treatments for FOP exist, but interim phaseIII MOVE trial (NCT03312634) results suggest marked efficacy for palovarotene (PVO). 1 The PIVOINE rollover trial (NCT05027802) has been designed to allow treatment continuity and further evaluation of PVO safety and efficacy; the methodology is given here. Methods Patients will receive 5 mg PVO daily, or the parent study completion dose, for a maximum of 3 years; during flare-ups, patients will receive 20 mg daily for 4 weeks, then 10 mg daily for 8 weeks. Enrollment criteria: completion of a parent study (end of study/treatment visit of NCT03312634 or NCT02279095/NCT02979769), ≥14 years of age, full skeletal maturity if aged <18 or deemed to be final adult height. PIVOINE aims to enroll 61 patients; recruitment has not begun. The primary outcome will be the incidence and description of all treatment-emergent adverse events, collected continuously over the study period. Secondary outcomes (collected every 6 months; reported as raw values and change from the inclusion visit for outcomes specified by *) include: range of motion* (using Cumulative Analogue Joint Involvement Scale total score), the use of aids, assistive devices and adaptations*, physical function* (using adult form of the FOP-Physical Function Questionnaire; total score and upper extremities and mobility sub-scores), the frequency of healthcare utilization, and physical and mental health* (using Patient Reported Outcomes Measurement Information System Global Health Scale). Lung function will be assessed via observed and percentage predicted (PP) forced vital capacity (FVC)*, forced expiratory volume in 1 second (FEV 1)*, diffusion capacity of the lung for carbon monoxide*, and the absolute and PP FEV 1 /FVC ratio*. The number of investigator-reported flare-ups*, including duration and outcomes, will be reported along with the percentage of patients with new bone growth. Summary Results from PIVOINE, estimated to end in November 2024, will allow further evaluation of PVO in FOP.