Background: An accurate measurement of disease activity is essential for the appropriate management of a patient with rheumatoid arthritis (RA). Hematological markers of systemic inflammation (Neutrophil-to-Lymphocyte (NLR), Platelet-to-Lymphocyte (PLR) and Lymphocyte-to-Monocyte (LMR) ratios) are reported to be novel, sensitive measures of inflammatory response, in addition to conventional markers (erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Disease Activity Score (DAS28)). The goal of the study was to assess the relationship of NLR, PLR, and LMR with ultrasonography (US) parameters of disease activity in RA patients. Methods: The study group consisted of 126 consecutive RA patients (100 women, 26 men). The following assessments were performed: joint counts, DAS28, complete blood cell counts, ESR, CRP, and US of 24 small joints. Results: NLR and PLR were significantly positively correlated with all US parameters of disease activity (Grey Scale US, Power Doppler US, and Global scores). The mean values of NLR and PLR were significantly higher in patients with poor prognostic factors: moderate/high vs. low disease activity (NLR: p < 0.001; PLR: p = 0.007), anti-CCP positive vs. anti-CCP negative (NLR: p = 0.01; PLR: p = 0.006). In multiple regression tests, significant correlations were confirmed for: NLR and DAS28 (p = 0.04), and CRP (p = 0.001); PLR and Power Doppler US (p = 0.04), and ESR (p = 0.02). No correlation was found for LMR. Conclusion: NLR and PLR are associated with US disease activity parameters and may serve as reliable, inexpensive markers, with prognostic significance in RA.