The present paper looks at the effect of sleeper separation on rail corrugation growth. The case under study involves short pitch corrugations on the low rail in sharp bends, the bends in question being those of metro-type railways in Bilbao, with the track on concrete slabs and with two resilient stages of STEDEF type. With an initial sleeper separation of 1000 mm, corrugation depths measured up to 0.42 mm peak-to-peak after the passing of only 920,000 wheelsets. Following the replacement of corrugated rails with new ones, vertical and transversal accelerations on the low rail were compared above sleepers, and at mid-span, while trains passed by. With a separation distance of 1000 mm there is, at the mid-span, a sizable response at 204 and 244 Hz that is not present above the sleepers. With the insertion of intermediate sleepers, hence reduction of separation to 500 mm, corrugation growth was found to cease. The results described in this paper derive from two years' observation.