Purpose: Lymphoproliferative neoplasms are the largest and most frequently diagnosed entities in the group of haematological malignancies. The aim of the study was to assess whether apparent diffusion coefficient (ADC) measured on the first day of the second cycle of chemotherapy could be a predictor of prognosis and of the final treatment's outcome. Material and methods: The study included 27 patients with diagnosed Hodgkin's and non-Hodgkin's lymphoma, who had magnetic resonance (MR) performed with diffusion weighted imaging/apparent diffusion coefficient (DWI/ADC) before and on the first day of the second cycle of chemotherapy. Imaging was performed using a 1.5 T MR scanner. ADC was measured in lymphoma infiltration in the area of the lowest signal in the ADC map and the highest signal on b 800 images in post-treatment study. After that, the corresponding area was determined in a pre-treatment study and an ADC value was measured. Results: The difference between ADC values in pre-treatment (ADC = 720 mm2/s) and post-treatment (ADC = 1059 mm2/s) studies was statistically significant (p < 0.001). Cutoff values for estimating response to treatment were established at the level of ADC 1080 mm2/s, and ADC to muscle ratio at 0.82 in post-treatment study. Patients with ADC > 752 mm2/s before treatment manifested lower probability of progression than patients with ADC < 752 mm2/s. Conclusions: ADC measurement's before treatment and on the first day of the second cycle of chemotherapy can be used as a prognostic marker in lymphoma therapy. ADC values lower than 1080 mm2/s and an increase of the ratio after the treatment can be considered as a marker of disease progression.