This paper describes the results of seismic refraction investigations of the upper crustal structure in the area of Deception Island, West Antarctica, which were made during the Polish Antarctic Geodynamical Expeditions in 1979-80 and 1987-88. In the caldera and immediate vicinity of Deception Island a layer of unconsolidated and poorly consolidated young sediments of 1.9–2.2 km s−1 P-wave velocity was found. Velocities of 4.1–4.3 km s−1 were found in the depth interval from 0.6–1.3 to about 3 km. Lateral differences in upper crustal structure between the south-eastern and western sectors were identified. In the region between Deception and Livingston islands an inclined boundary with a velocity of about 6.1 km s−1 occurs. A deep fault zone dividing crustal blocks beneath Deception Island is associated with a prominent volcanic line within Bransfield Strait extending between Deception and Bridgeman islands.