To determine the frequency of care complexity individual factors documented in the nursing assessment and to identify the risk factors associated with hospital readmission within 30 days of hospital discharge. Observational analysis of a retrospective cohort at a 700-bed university hospital in Barcelona, Spain. A total of 16,925 adult patient admissions to a ward or intermediate care units were evaluated from January to December 2016. Most patients were admitted due to cardiocirculatory and respiratory disorders (29.3%), musculoskeletal and nervous system disorders (21.8%), digestive and hepatobiliary conditions (17.9%), and kidney or urinary disorders (11.2%). Readmission was defined as rehospitalization for any reason within 30 days of discharge. Patients who required hospital readmission were compared with those who did not. The individual factors of care complexity included five domains (developmental, mental-cognitive, psycho-emotional, sociocultural, and comorbidity or complications) and were reviewed using the electronic nursing assessment records. Multivariate logistic analysis was performed to determine factors associated with readmission. A total of 1,052 patients (6.4%) were readmitted within 30 days of hospital discharge. Care complexity individual factors from the comorbidity or complications domain were found to be the most frequently e-charted (88.3%). Care complexity individual factors from developmental (33.2%), psycho-emotional (13.2%), mental-cognitive (7.2%), and sociocultural (0.7%) domains were less frequently documented. Independent factors associated with hospital readmission were old age (≥75 years), duration of first hospitalization, admission to a nonsurgical ward, major chronic disease, hemodynamic instability, immunosuppression, and relative weight of diagnosis-related group. A substantial number of patients required readmission within 30 days after discharge. The most frequent care complexity individual factors recorded in the nursing assessment at index admission were related to comorbidity or complications, developmental, and psycho-emotional domains. Strategies related to transition of care that include clinical characteristics and comorbidity or complications factors should be a priority at hospital discharge and after leaving hospital, but other factors related to developmental and psycho-emotional domains could have an important effect on the use of healthcare resources. Nurses should identify patients with comorbidity or complications, developmental, and psycho-emotional complexity factors during the index admission in order to be able to implement an effective discharge process of care.