Report on a programme of archaeological monitoring and recording conducted on the groundworks for a new dwelling on land at 20 Willoughby Road, Boston. A layer of alluvial silts, likely the result of flooding of the area, was sealed by a number of dumped deposits of Medieval to post-Medieval date. These are likely to relate to the digging, widening and dredging of the nearby Maud Foster Drain. Finds recovered from these deposits included Medieval pottery, roof tile and architectural stone fragments, possibly from the former Hospital of St Leonard, which is believed to have existed on the site of the extant St Leonard's Bedehouses.