We performed bilateral ultrasound-guided erector spinae plane blocks at the second and eighth thoracic vertebrae in 11 fresh frozen cadavers. Methylene blue dye spread variably and extensively deep to the erector spinae muscles fascia with involvement of the spinal rami and paravertebral space in 1 of 11 cadavers when injected at the eighth thoracic vertebra, and in 4 of 11 cadavers at the second thoracic vertebra, with crossover to the contralateral side of the spine. Our study demonstrates that in cadavers, an erector spinae plane block follows the fascial planes with unpredictable spread, which might explain its varying clinical efficacy.