The aim of this prospective study was to evaluate if atrophy of the plantar fat pad in splay-foot deformities was a major cause of metatarsalgia. A sonographic method of measuring the thickness of the plantar fat pad under the second and third metatarsal heads was developed. The method was tested on 25 volunteers and the intraobserver reliability was calculated to be 97.1% for the second metatarsal and 96.7% for the third metatarsal. Sonographic measurement of the plantar fat pad was then performed on 100 symptomatic feet Pain frequency and pain intensity were determined by using a verbal rating scale (VRS) and a visual analog scale (VAS). The intermetatarsal angle 1/2 was measured and then compared to the thickness of the fat pad for each patient. A correlation between the increase of the intermetatarsal angle and the decrease of the fat pad thickness could not be demonstrated (r = 0.041). The frequency of metatarsalgia did not correlate with a decrease of the thickness of the plantar fat pad under the second metatarsal head (t statistic: 1.978; Durbin-Watson test: 1.999; p value = .0507) and the third metatarsal head (t statistic: 3.199; Durbin-Watson test: 1.962; p value = .0019). The pain intensity showed a similar lack of correlation with the thickness of the plantar fat pad under the second metatarsal head (t statistic: 1.828; Durbin-Watson test: 2.365; p value = .0706) and the third metatarsal head (t statistic: 1.846; Durbin-Watson test: 2.371; p value = .0678). This study shows that a splay-foot deformity is not associated with a decrease of the thickness of the plantar fat pad. Furthermore, alterations of the thickness of the plantar fat pad are not relevant to the intensity and frequency of metatarsalgia.