The structure ofcis-2-phenylcyclobutanecarboxylic acid (1) andcis-3-(p-fluorophenyl)cyclobutanecarboxylic acid (2) have been determined by X-ray diffraction methods. Crystals of1are monoclinic, space groupC2/cwitha = 15.420(8),b = 11.687(6),c = 11.226(5) Å, β = 112.45(4)°, and eight molecules in the unit cell. Crystals of2are monoclinic, space groupP21/n,a = 8.038(5),b = 5.405(4),c = 22.69(1) Å, and β = 97.30(4)°, with four molecules in the unit cell. In both compounds the cyclobutane ring is puckered, with dihedral angles of 27° and 31°. The bond joining the substituted ring atoms in1is significantly longer (1.581(2) Å) than the other three (average 1.535(2) Å), due to crowding of substituents. In2both the carboxyl and phenyl substituents are close to the bisecting geometry, whereas in1both substituents deviate from this conformation, the carboxyl more than the phenyl.