Among instruments measuring spiritual well-being, the Functional Assessment of Chronic Illness Therapy-Spiritual well-being (FACIT-Sp-12) is the most widely used instrument in research. It has been validated in patients suffering from cancer or HIV/AIDS, but has rarely been used in elderly patients. The objectives of this study were to determine the psychometric properties and suitability of the FACIT-Spto assess spiritual well-being in hospitalized elderly patients. This cross-sectional study uses a mixed method approach. Subjects were patients (N = 208), aged 65 years and older, consecutively admitted in post-acute rehabilitation. Psychometric properties of the FACITSp were investigated. The internal structure of the FACIT-Sp (factor structure and internal consistency) was assessed. Convergent validity of the FACIT-Sp was assessed using the Spiritual Distress Assessment Tool (SDAT), the question "Are you at peace?" and the Geriatric Depression Scale (GDS). Predictive validity was assessed using length of stay (LOS) and discharge destination. Understanding and interpretation of FACIT-Sp items were consecutively assessed in a sub-sample of 135 patients. Results show that FACIT-Sp scores ranged from 7 to 46 (mean 29.6 ± 7.8); 23.1% of the patients had high spiritual well-being. Cronbach's α was g ood ( 0.85). Item-to-total correlations were all significant (0.34 to 0.73). Principal component analyses performed with 2 or 3 factors were only moderately consistent with previous work. FACIT-Sp correlated with SDAT, "Are you at peace?" and GDS (Rho = −0.45, P < 0.001; 0.51, P < 0.001 and −0.38, P < 0.001). No association was found with LOS or discharge destination. Spontaneous comments about one or more FACIT-Sp items were made by 97/135 (71.9%). Specifically, items that address purpose and meaning in life were frequently found difficult to answer. Analyses suggest that the FACIT-Sp may underestimate spiritual well-being in older patients. In conclusion, despite having acceptable psychometric properties, the FACIT-Sp presents limitations for measurement of spiritual well-being in hospitalized elderly patients.