In this prospective study the impact of fatty liver and an impaired liver function on the treatment outcome of displacement of the abomasum (DA) was investigated. In a yearlong period, all cows suffering from DA submitted to the clinic were included in this study. All cows were clinically examined before surgery and a serum sample was taken to measure the following parameters: ASAT, bilirubin, urea. Liver biopsy was performed in all cows. Liver fat content was measured gravimetrically and concentrations of triglycerides were measured using a commercial test kit. Reposition of DA was done using the method by Dirksen. A total of 365 cows with DA entered the study, 326 (89.3%) suffered from LDA and 39 (10.7%) from RDA. RDA-cows had significantly (p = 0.002) more days in milk than LDA-cows. RDA-cows had significantly (p < 0.001) higher urea concentrations than LDA-cows. Bilirubin concentrations (p = 0.008) and liver fat content, triglyceride concentrations and the ratio of triglycerides to fat (TRI/FAT) (p < 0.001) were significantly higher in LDA-cows. The majority of LDA-cows showed at least a mild fatty liver. Comparing the cows with successful and failed treatment showed that ASAT-activity (p = 0.021), bilirubin concentration (p = 0.001), triglyceride concentration in liver and TRI/FAT (all p < 0.001) were significantly higher in the unsuccessfully treated cows. In RDA cows, significant differences between successfully and unsuccessfully treated cows were only seen in urea concentration (p = 0.004). ROC-analysis was performed to determine whether any parameter is suitable for a prediction of treatment outcome. In RDA-cows no threshold value was traceable for urea concentration. In LDA cows, TRI/FAT showed the best curve progression. The threshold value of 53.5 % had a sensitivity of 0.720 and a specificity of 0.700. LDA-cows exceeding this threshold had a 2.4 higher risk of an unsuccessful treatment. Due to the good overall treatment success (92.3 %) the positive predictive value for an unsuccessful or ineffective treatment was 0.368 only. The results of our study clearly show that impaired liver function plays an important role in the outcome of treatment of LDA but not RDA. In spite of this no laboratory parameter provides sufficient power to make a predictive statement of treatment outcome.