The Behavior and Symptom Identification Scale 24 (BASIS-24) is a psychiatric outcome measure used for inpatient and outpatient populations. This 24-item measure comprises six subscales: depression/functioning; interpersonal relationships; self-harm; emotional lability; psychosis; and substance abuse. Earlier studies examined the reliability and validity of the BASIS-24, but none empirically examined its factor structure across gender. The purpose of this study was therefore to assess the construct validity of the BASIS-24 six-factor model and find evidence of configural, metric, strong and strict factorial invariance across gender. The sample consisted of 1398 psychiatric inpatients that completed BASIS-24 at admission and discharge at 11 facilities nation-wide. Confirmatory factor analyses were used to test measurement invariance of the BASIS-24 six-factor model across males and females. The single confirmatory factor analysis showed the original six-factor model of BASIS-24 provided an acceptable fit to the male sample at admission (RMSEA=0.058, SRMR=0.070, CFI=0.975, NNFI=0.971 and GFI=0.977) and at discharge (RMSEA=0.059, SRMR=0 .078, CFI=0.977, NNFI=0.972, and GFI=0.969). The goodness-of-fit indices for the female group at admission (RMSEA=0.055, SRMR=0.067, CFI=0.980, NNFI=0.976, and GFI=0.983), and at discharge (RMSEA=0.055, SRMR=0.079, CFI=0.98, NNFI=0.977, and GFI=0.971) also revealed that the six factor model fit reasonably well to the data. The goodness-of-fit indices between the unconstrained and constrained models showed that all four multi-group models were equivalent for both male and female samples at admission and discharge in terms of goodness-of-fit examined through the ΔCFI and that all of them show an acceptable fit to the data. The decrease in CFI was <0.008 for admission sample and <0.003 for discharge sample and both fell below the 0.01 cut-off. This indicates that the configural, metric, as well as the strong and strict factorial invariance of BASIS-24 exist across males and females. The two important contributions of the present study are: 1) BASIS-24 can be used as a reliable and valid symptom measurement tool in assessing psychiatric inpatient populations which can compare quantitative differences in the magnitude of patient symptoms and functioning across genders; 2) the current study provides an example of useful statistical methodology for examining specific questions related to factorial invariance of the BASIS-24 instrument across gender. Implications of social work practice and research are discussed.