Mutations in the mitochondrial cardiolipin (CL) transacylase, tafazzin (Taz1p), result in the X-linked cardioskeletal myopathy, Barth syndrome (BTHS). The mitochondria of BTHS patients exhibit variable respiratory defects and abnormal cristae ultrastructure. The biochemical basis for these observations is unknown. In the absence of its target phospholipid, CL, a very large Taz1p complex is missing, whereas several discrete smaller complexes are still observed. None of the identified Taz1p complexes represents Taz1p homodimers. Instead, yeast Taz1p physically assembles in several protein complexes of distinct size and composition. The ATP synthase and AAC2, both required for oxidative phosphorylation, are identified in separate stable Taz1p complexes. In the absence of CL, each interaction is still detected albeit in reduced abundance compared with when CL is present. Taz1p is not necessary for the normal expression of AAC2 or ATP synthase subunits or assembly of their respective complexes. In contrast, the largest Taz1p complex requires assembled ATP synthase and CL. Mitochondria in Delta taz1 yeast, similar to ATP synthase oligomer mutants, exhibit altered cristae morphology even though ATP synthase oligomer formation is unaffected. Thus, the Taz1p interactome defined here provides novel insight into the variable respiratory defects and morphological abnormalities observed in mitochondria of BTHS patients.