Sentiment analysis may offer insights into patient outcomes through the subjective expressions made by clinicians in the text of encounter notes. We analyzed the predictive, concurrent, convergent, and content validity of six sentiment methods in a sample of 793,725 multidisciplinary clinical notes among 41,283 hospitalizations associated with an intensive care unit stay. None of these approaches improved early prediction of in-hospital mortality using logistic regression models, but did improve both discrimination and calibration when using random forests. Additionally, positive sentiment measured by the CoreNLP (OR 0.04, 95% CI 0.002 - 0.55), Pattern (OR 0.09, 95% CI 0.04 - 0.17), sentimentr (OR 0.37, 95% CI 0.25 - 0.63), and Opinion (OR 0.25, 95% CI 0.07 - 0.89) methods were inversely associated with death on the concurrent day after adjustment for demographic characteristics and illness severity. Median daily lexical coverage ranged from 5.4% to 20.1%. While sentiment between all methods was positively correlated, their agreement was weak. Sentiment analysis holds promise for clinical applications but will require a novel domain-specific method applicable to clinical text.