BACKGROUND: Proximal femoral fractures (PFFs) are a public health issue due to their high frequency. The frequency of a second PFF on the other side is estimated at 10%. This estimation is controversial, however, and the risk factors have not been evaluated in a large population of French patients. The objective of this retrospective case-control study was to determine: (1) the incidence of second PFFs and (2) their risk factors.HYPOTHESIS: The incidence of second PFFs is >2% after 1 year and >5% after 3 years.MATERIAL AND METHODS: We conducted a case-control study in a population of consecutive patients managed surgically for PPF at the Lyon Sud Hospital between 2013 and 2014. We analysed the following clinical factors: age, sex, body mass index (BMI), institutionalisation, the Parker score, the American Society of Anesthesiologists score (ASA), comorbidities, and the use of psychoactive drugs.RESULTS: We included 474 PFFs (trochanter, n=240 and neck, n=234) of which 36 were bilateral. The contralateral fracture occurred within 1 year of the first fracture in 6/474 (1.3%) cases and within 3 years in all 36 cases (7.6%). The case-control study comprised 49 cases with bilateral PFF and 161 controls with no second hip fracture within 3 years. Risk factors for a second hip fracture were age older than 90 years (odds ratio [OR]=5.44; 95% confidence interval [95%CI], 112-2642 (p=0.002)) and a history of heart disease (OR, 2.18; 95%CI, 1.06-4.47 [p=0.03]). A Parker score?6 was protective (OR, 0.84; 95%CI,0.71-0.99 [p=0.03]). Mortality after 3 years was 42% (201/474), and 13% (63/474) of patients were lost to follow-up.DISCUSSION: Age older than 90 years, a Parker score below 6, and a history of heart disease are risk factors for a second PFF within 3 years after the first PFF.LEVEL OF EVIDENCE: III; case-control study.