Angioimmunoblastic T-cell lymphoma (AITL) is an infrequent subtype of peripheral T-cell lymphoma derived from follicular helper T cells. Recently, a somatic G17V RHOA gene mutation has been reported. In this article, we examined the RHOA G17V mutation in 18 cases of AITL by 3 different techniques of Sanger sequencing, fully automated SNP genotyping, and deep sequencing, using routine diagnostic formalin-fixed paraffin-embedded tissue. The RHOA G17V mutation was detected in 10 cases (56%). Among the 10 mutated cases, 8 cases were detected by all 3 methods. The status of RHOA mutation was subsequently compared with the clinicopathologic characteristics of AITL. RHOA-mutated AITL (10 cases) was clinically characterized by high serum IL-2R and a poor ECOG performance status. By immunohistochemistry, expression of CD10, PD-1, CXCL13, and CCR4 and a wide distribution of CD21(+) follicular dendritic cells were observed in RHOA-mutated cases. Among these, CCR4 expression and the CD21(+) network in RHOA-mutated AITL cases were more extensive than in the RHOA mutation-negative AITL cases (P<0.05). Thus, RHOA-mutated AITL cases are more characteristic of follicular helper T cells, and the presence of such a mutation is an important marker for AITL.