BACKGROUND: Recent literature has indicated altitude may be a protective factor for concussion but it is unknown whether altitude or heat index affects recovery. OBJECTIVE: To examine whether on-field heat index and altitude at the time of injury alter acute (< 48 h) concussion assessments, days-to-asymptomatic, and days-to-return-to-play in collegiate athletes following concussion. METHODS: Collegiate athletes (n = 187; age = 19.7 +/- 1.4 years; male = 70.6%) underwent baseline assessments across 30 universities and experienced a concussion in this retrospective cohort study. Altitude (m) and heat index ( degrees C) at the time and location of injury were determined using valid online database tools. Acute concussion assessments included the Sport Concussion Assessment Tool (SCAT) symptom inventory, Balance Error Scoring System (BESS), and the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). We used multiple linear regression models to determine whether heat index and altitude predicted each acute assessment outcome, days-to-asymptomatic, and days-to-return-to-play. RESULTS: Collegiate athletes were concussed at a 181.1 m (range - 0.6 to 2201.9 m) median altitude and 17.8 degrees C (range - 6.1 to 35.6 degrees C) median heat index. Altitude did not predict (p >/= 0.265) any outcomes. Every one-degree increase in heat index reduced days-to-asymptomatic (p = 0.047; R(2) = 0.06) and days-to-return-to-play (p = 0.006; R(2) = 0.09) by 0.05 and 0.14 days, respectively. Heat index and altitude did not explain significant variance in SCAT, BESS, and ImPACT composite scores (p’s = 0.20-0.922). CONCLUSION: Our findings suggest that on-field altitude and heat index at the time of injury do not contribute to clinically meaningful changes on acute assessments or concussion recovery. On-field altitude and heat index do not appear to significantly alter assessment outcomes or clinical recovery, suggesting that environmental factors at altitudes below < 2500 m are negligible outcomes for researchers and clinicians to consider post-concussion.