The relationship between structural distortions and resistivity in pulsed laser deposited La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3MnO3 (LSMO) thin films was investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM) and resistivity measurements. The growth defects inherent to annealed films were characterized, and then additional defects were introduced by radiation damage. Epitaxially grown films on (100) LaA1O3 substrates exhibited three primary types of growth defects: interface strain, column boundary mismatch, and column rotation. High resolution TEM measurements show well-ordered regions of film that offer low resistance paths for current flow around growth defects. A series of annealed samples were irradiated with 6 Mev Si+3 ions to produce 0.006 to 0.024 displacements per atom (dpa) in LCMO films, and 0.028 to 0.14 dpa in LSMO films. The peak resistance temperature (Tp) was found to depend strongly on defect concentration, varying from 235K ± 15K for the unirradiated LCMO films to 95K for 0.018 dpa. At 0.024 dpa, the LCMO film was insulating at all temperatures. LSMO films showed a downward shift in Tp from 300K for an unirradiated film to 250K for 0.028 dpa, and complete insulating behavior for 0.14 dpa.