Defect formation has been studied in nitrogen-implanted III-V compound semiconductor material InP. Sulphur-doped n-type (100) InP samples were implanted at room temperature with 30 keV 15N+ion doses of 10 power in14 - 10 power in 16 N atoms cm-2. The implanted samples were subjected to isochronal vacuum annealing in the temperature range of 450-650 °C. The annealing behavior of nitrogen atom distributions, implantation-induced displacements of indium atoms, vacancy-type defects, and damage annealing were studied by nuclear resonance broadening, secondary ion mass spectrometry, ion backscattering and channeling, and slow positron annihilation techniques. Doses above 10 power in 15 N atoms cm-2 were found to produce amorphous layers extending from the surface to depths beyond the deposited energy distribution, up to 110 nm. The depth of an amorphous layer was observed to depend on the implantation dose. Temperature and dose-dependent epitaxial regrowth starting from the amorphous-crystalline interface was observed at 575 °C. The damage and vacancy concentration distributions were correlated with the implanted nitrogen distribution in the case of the highest implantation dose at 10 power in 16 N atoms cm-2 ; disorder annealing and loss of nitrogen behave in a like manner with increasing temperature. For the lower doses, however, almost no redistribution or loss of nitrogen arose despite structural damage and vacancy annealing. Interpretation of the positron data allowed an identification of two types of vacancies. The type of the vacancy defects was found to depend on the implantation dose and annealing temperature; mono-vacancies were formed in the In sublattice at the low implantation doses, while the highest dose produced divacancies. The annealing tended to convert the mono-vacancies into divacancies, which were recovered at high temperatures depending on the implantation dose.