To correlate tumour grading and prognostic immunohistochemical markers of lung cancer with simultaneously acquired standardised uptake values (SUV) and apparent diffusion coefficient (ADC) derived from hybrid PET/MRI. In this retrospective study, 55 consecutive patients (mean age 62.5±9.2years) with therapy-naïve, histologically proven lung cancer were included. All patients underwent whole-body PET/MRI using 18F-flourdeoxyglucose (18F-FDG) as a radiotracer. Diffusion-weighted imaging of the chest (DWI, b-values: 0, 500, 1000s/mm2 ) was performed simultaneously with PET acquisition. Histopathological tumour grading was available in 43/55 patients. In 15/55 patients, immunohistochemical markers, that is, phospho-AKT Ser473 (pAKTS473), phosphorylated extracellular signal-regulated kinase (pERK), phosphatase and tensin homolog (PTEN), and human epidermal growth factor receptor 2 (erbB2) were available. The average SUVmax, SUVmean, ADCmin and ADCmean in lung cancer primaries were 12.6±5.9, 7.7±4.6, 569.9±96.1s/mm2 and 825.8±93.2s/mm2 , respectively. We found a significant inverse correlation between the ADCmin and SUVmax (r=-0.58, P<0.001) as well as between the ADCmin and SUVmean (r=-0.44, P<0.001). Tumour grading showed a significant positive correlation with SUVmax and SUVmean (R=0.34 and R=0.31, both P<0.05) and a significant inverse correlation with ADCmin and ADCmean (r=-0.30 and r=-0.40, both P<0.05). In addition, erbB2 showed a significant inverse correlation with SUVmax and SUVmean (r=-0.50 and r=-0.49, both P<0.05). The other immunohistochemical markers did not show any significant correlation. 18F-FDG-PET/MRI showed weak to moderate correlations between SUV, ADC, tumour grading and erbB2-expression of lung cancer. Hence, 18F-FDG-PET/MRI may, to some extent, offer complementary information to the histopathology of lung cancer, for the evaluation of tumour aggressiveness and treatment response.