It is known that there is an association between gastrocnemius tightness and plantar fasciitis, but this has never been quantified. The purpose of the study was to determine the correlation between gastrocnemius tightness and the severity of heel pain in plantar fasciitis. Thirty-three patients were prescribed physiotherapist-directed gastrocnemius stretching exercises, a Strassburg Sock or night splint, and silicone heel insoles as required. Outcome measures included (1) gastrocnemius tightness, (2) 100-mm visual analog scale (VAS) for pain on the first steps in the morning, and (3) 100-mm VAS for the worst pain felt during the previous week. Gastrocnemius tightness was measured by the difference in maximal ankle dorsiflexion between knee bent and straight with a goniometer. The mean gastrocnemius tightness was 22 degrees at baseline compared with 9 degrees at the final follow-up (P < .01). A reduction in VAS for pain on the first steps in the morning and VAS for the worst pain felt during the previous week from baseline to final follow-up was observed (P < .01). Correlation analysis of 105 data points between gastrocnemius tightness and VAS for pain on the first steps in the morning was R = 0.757 (P < .001), and between gastrocnemius tightness and VAS for the worst pain felt during the previous week was R = 0.781 (P < .001). The study observed a strong, statistically significant correlation between gastrocnemius tightness and the severity of heel pain in plantar fasciitis. Level IV, case series.