The Longest Day of Nelson is an amateur 24-hour automobile endurance race sanctioned by the Sports Car Club of America (SCCA) at Nelson Ledges Road Course in Ohio. The event takes place on or near the summer solstice each year. The host of the event was the Northeast Ohio Region of the SCCA. In 2004, 2005, and 2006, 12-hour races were held.
A 24-hour motorcycle race was also held at the circuit, ceasing in 1993.
It is one of three events that comprise the Triple Crown of SCCA amateur endurance racing. The second event in the Triple Crown, The 12 Hours at the Point, held at Summit Point Raceway in West Virginia. The final member of the crown is disputed; the Charge of the Headlight Brigade, held at Virginia International Raceway in Virginia or the Tropical 12 Hour, held at Homestead-Miami Speedway in Florida both lay claim to the event.