However, there is little information available on the atomic structure and electronic properties of AlInP surfaces. It has been noted that different growth conditions lead to different degrees of CuPt ordering in the bulk material , i.e., alternating group III layers perpendicular to the or ] directions. This is likely to be related to the formation of surface dimers, which induce strain in the material . Very recently, some models for clean AlInP(001) surfaces were established, which show that structures different from the ones known from binary III-V(001) surfaces may occur . However, this study was restricted to clean surfaces. Often, AlInP is grown by metal organic vapor phase epitaxy (MOVPE) and chemical beam epitaxy (CBE). Since hydrogen is present in MOVPE and CBE, it can be expected to be present at the AlInP surface as well . Therefore, we here extend the previous study to account for the possibility of surface adsorbed hydrogen. A systematic search for stable Al 0.5 In 0.5 P(001) surface structures is performed, where the existence of hydrogen is considered as an additional degree of freedom. The initial geometries for structure optimization are generated by systematically varying the surface stoichiometry of both CuPt-A and CuPt-B type ordered Al 0.5 In 0.5 P crystals. Altogether, more than 80 surfaces are probed computationally. The computational predictions for typical MOVPE growth conditions are compared with low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) data measured on epitaxially grown Al 0.52 In 0.48 P(001) samples.