The authors have developed a swing-shell closure with fourbar linkage that combines the advantages of the familiar bivalve with flexible overlap designs. Like the conventional hinged bivalve or “alligator-mouth” design, the swing shell has a rigid anterior panel that provides consistent weightbearing contours and positive vertical suspension. Like the flexible overlap system, the swing shell also offers ease of donning and accommodates volume changes. These advantages justify the added fabrication time, particularly when atrophy or growth is anticipated. Encouraging results in 24 of 25 orthotic cases led to the successful incorporation of the design into 15 prostheses for congenital anomalies.