To assess the inter- and intra-observer reproducibility of musculoskeletal ultrasonography among rheumatologist in detecting inflammatory and morphostructural changes in small joints of the hands in patients with rheumatoid arthritis (RA). Five members of the "Escuela de Ecografía del Colegio Mexicano de Reumatología" tested their inter- and intra-observer reliabilities in the assessment of basic sonographic findings of joint inflammation and bone erosion. Their results were compared to those obtained by a group of international experts from European League Against Rheumatism. A clinical rheumatologist evaluated eight RA patients. Five Siemens Acuson Antares ultrasound machines (7-13 MHz linear probes) were used. The OMERACT preliminary definitions of joint effusion, synovial hypertrophy, bone erosions and tenosynovitis were adopted. Inter-observer and intra-observer agreement was calculated by overall agreement and kappa statistics. Mean kappa value for joint effusion was good, 0.654 (85%); synovial hypertrophy, 0.550 (77.2%); power Doppler signal, 0.550 (82.5%); bone erosions, 0.549 (81%); and tenosynovitis, 0.500 (91.5%). Mean and overall intra-observer agreement for semiquantitative score was good for joint effusion, 0.630 (77.2%) and bone erosions, 0.605 (56.25%); and moderate to synovial hypertrophy, 0.476 (65%) and power Doppler signal, 0.471 (80%). Mean kappa value for joint effusion was 0.381 (95%), synovial hypertrophy, 0.447 (72%); power Doppler signal, 0.496 (81%); bone erosions, 0.294 (81%); and tenosynovitis, 0.030 (66%). Mean and overall inter-observer agreement for semiquantitative score was poor for joint effusion, 0.325 (57%) and bone erosions, 0.360 (43%); and moderate to synovial hypertrophy, 0.431 (55%) and power Doppler signal, 0.496 (81%). Intra-observer variability reached the highest levels of agreement. Factors related to the experience of the rheumatologist, the time spent in each examination and knowledge of the software ultrasound equipment could influence the lower level of inter-observer agreement in this study.