Objectives To establish the correlation between number of ACR classification criteria, as well as disease duration with disease activity index (SELENA SLEDAI) and damage index (SLICC/ACR damage index) and to determine the correlation between laboratory findings of disease activity and their combinations (complement components, CRP, anti-dsDNA antibodies) with disease activity index (SELENA SLEDAI) and damage index (SLICC/ACR damage index). Patients and Methods In this cross-sectional study that was conducted at the Department of rheumatology and clinical immunology CHC Rijeka 110 patients with clear diagnosis of SLE who fulfilled 4 or more ACR classification criteria were included. This patients were in a regular physician's control and all of them were examined consequently during the period of three-months, respectively in a period from September to November 2013. In all patients we recorded general data (age, disease duration, gender) and number of ACR classification criteria. Disease activity was assessed by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and severity by Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) damage index. In all patients we determined laboratory and immunology parameters of disease activity (CRP, C3, C4 complement components, anti-dsDNA). Results The average age of our patients at the time of conducting the study was 47±14 years, while average disease duration was 10±7 years. Women were more affected than men (n=97/13, 88%/12%). The average total number of fulfilled ACR classification criteria was 5±1. The most common ACR classification criterion at the time of conducting the study was the positive ANA titer. Other most frequently present ACR classification criteria were as follows: immunology disorder, non-erosive arthritis, hematological disorder, malar rash, renal disorder, serositis and photosensitivity, oral ulcers, neurological disorder and discoid rash. In 33% of our patients was detected presence of active disease (SELENA SLEDAI score ≥6). A significantly higher values of SLICC/ACR damage index were detected in men compared to women. A weak, positive correlation between number of ACR classification criteria and SELENA SLEDAI disease activity index was detected. Correlation between number of ACR VIII classification criteria and SLICC/ACR damage index was not observed. The presence of good and positive correlation was detected between disease duration and SLICC/ACR damage index but with no correlation between disease duration and SELENA SLEDAI disease activity index. Analysis of correlation between laboratory and immunology parameters showed presence of weak negative correlation between C3 and C4 complement components and categorized values of anti-dsDNA antibodies. Less strong, but also existing correlation was detected between values of CRP and anti-dsDNA antibodies. A good, significant and negative correlation was observed between C3 complement component and SELENA SLEDAI disease activity index. Also, a good, significant and positive correlation was detected between CRP value and number of SELENA SLEDAI components. A very strong correlation was detected between categorised values of anti-dsDNA antibodies and SELENA SLEDAI disease activity index. Between value of CRP and SLICC/ACR damage index a good and positive correlation was detected. Conclusion In our study we showed that the number of fulfilled ACR classification criteria in patients with systemic lupus erythematosus correlates weak with disease activity index (SELENA SLEDAI) and it is not associated with SLICC/ACR damage index. Greater disease duration in SLE patients is associated with higher SLICC/ACR damage index, but on the other hand, does not correlate with SELENA SLEDAI disease activity index.