The primary purpose of this clinical study was to compare architectural metric parameters using microcomputed tomography (micro-CT) between sites grafted with blocks harvested from the mandibular ramus and calvarium for horizontal bone augmentation in the maxilla. The second aim was to compare the primary stability of implants placed in both types of block grafts. Ten consecutive healthy partially edentulous patients requiring extensive horizontal bone reconstruction in the maxilla were included. A total of 14 block grafts (7 each from the mandibular ramus and calvarium) were studied. After 4 to 6 months of healing, 41 implants were placed: 24 implants (58.5%) in calvarial (group 1) and 17 (41.5 %) in ramus grafts (group 2). A resonance frequency analysis (RFA) was performed to test implant stability. Furthermore, two biopsy specimens were randomly selected for histomorphometric analysis. Micro-CT analyses showed no significant difference in the morphometric parametric values analyzed between groups. Furthermore, RFA also showed no difference between groups. However, slightly higher RFA values were noted for implants placed in ramus grafts. Bone quality, as assessed by micro-CT and histomorphometric analyses, was similar in both ramus and calvarial block grafts. In addition, there was no difference in primary implant stability between groups.