A number of weighted smoothing splines were fit to data on carapace length and size-specific, median chela height of Paralomis formosa. The second derivative of the spline which made the best tradeoff between goodness of fit and smoothness was used as an estimate morphometric size at maturity. Bootstrapping techniques provided a bias-corrected estimate of morphometric size at maturity (sBc) equal to 80- carapace width, and Pr(72mm ≤ sBC ≤ 90mm) ≈ 0.95. The spline modeling technique appears to overcome some of the philosophical and statistical problems associated with estimating size at maturity by fitting linear models to log-transformed morphometric data (see Somerton 1980a and 1980b), but improvements could be made to make the spline technique more robust to outliers in Y-space (crabs with regenerating claws). Given the uncertainty in sBC and the lack of information about body size growth rates, a wide range of alternative size limits are likely to be feasible options for managing the P. formosa fishery, but, despite the availability of new data and the arbitrary nature of the current size limit on this species, there does not seem to be a sufficiently strong biological reason to revise the size limit regulation set forth in CM 91/XIV, Paragraph 10.