The objective of this study was to determine the length-length and length-weight relationships in Parapenaeus longirostris as a basis for conversions. Specimens were collected with hauls from the commercial trawler "Hapuloglu" between 9 and 12 December 2006 in Sigacik Bay and Kusadasi Bay in the Aegean Sea. Morphometric equations for the conversions of length and weight were constructed for females, males, and combined sexes. The equations for carapace length (CL), total length (TL), and body width (BW) for combined sexes were found as CL = 0.2296 x TL - 2.272, r(2) = 0.97, BW = 0.3708 x CL + 0.7694, r(2) = 0.91, and BW = 0.0861 x TL - 0.169, r(2) = 0.90, respectively. The length-weight relationship was determined as W = 0.0031 x TL3.108, r(2) = 0.98 for total length and W = 0.546 x CL2.743, r(2) = 0.97 for carapace length. Males were generally smaller than females (K-S test; p < 0.05) and size-frequency distributions (TL, CL, and BW) revealed differences between females and males (K-S test; p < 0.05). Various length-length and length-weight regressions were also found to differ with sex (F test; p < 0.05), except TL-CL (F = 0.40; p > 0.05).