Transmission electron microscopy (TEM) has been used to examine defects in diamond films grown by the microwave plasma-enhanced chemical vapor deposition (CVD) method. Graphite was used as the sole carbon source during the CVD process with silicon substrates. Growth defects including twins, stacking faults, dislocations and second-phase precipitates were observed in the films. In plan-view TEM, defect clusters at the centers of diamond grains were observed, where the film is also the thickest. Cross-sectional TEM was carried out to show that the defect clusters fan out from a single nucleation site in each grain, at the diamond-silicon interface. Possible growth mechanisms of the defect clusters in diamond grains are considered.