This study investigated the use of morphometric aspects of Aegla manuinflata Bond-Buckup and Santos, 2009 to determine the mean size of males and females at the onset of sexual maturity and to test for intraspecific sexual variations. The programs Mature I and Mature II were used to analyze relative growth. Relationships reflecting the onset of morphological sexual maturity were tested with the software REGRANS, as a means of comparing methodologies. The mean size at first maturity was estimated as 13.60 mm CL in males and 10.84 mm CL in females. The Principal Components Analysis showed that the dimensions of the chelipeds propodus length were primarily responsible for the total variance in the data for males and females. The Discriminant Function Analysis showed that there were no significant differences among juveniles; however, adult males and females were distinguished as two separate groups, indicating that sexual maturity in this species probably occurs after a single ecdysis. Aegla manuinflata shows heterochely, with the left cheliped being the larger in all categories. This seems to be a general pattern for members of Aeglidae.