The main goal of this study was to compare the telomere localizations, dynamics, and occurrences of telomere associations (TAs) in healthy cells, in tumor cells with active telomerase, and in tumor cells with mechanism of alternative lengthening of telomeres (ALT). These objectives were pursued by time-lapse microscopy of living cells and by visualizing telomeres with subtelomere DNA probes in repeated double-color fluorescence in situ hybridization (FISH) on 2D fixed nuclei. Samples were observed by high-resolution cytometry, and followed by image and statistical analysis of acquired data. As models for in situ experiments were chosen following lung tissue cell lines: cell line WI-38 (healthy lung fibroblasts), tumor cell line HT-1080 with active telomerase, and cell line WI-38 VA-13/2RA (VA-13) with ALT mechanism. For these studies were chosen telomeres of all acrocentric chromosomes (13q, 14q, 15q, 21q a 22q) and also p- and q-telomeres of similarly sized chromosomes 18 a 19, that differ in their localization in cell nucleus and in content of transcriptionaly active genes. As models for living-cells experiments were chosen following cell lines: U-2 OS (osteosarcoma ALT cell line) and HeLa (cervical carcinoma cell line with active telomerase). Distributions of radial distances of all in situ analyzed telomeres for all assessed cell lines are comparable in most cases with only several exceptions. Among these exceptions belongs shift of localization of telomere of chromosome 13 towards nuclear periphery in cell line VA-13 or localization of telomere of chromosome 15 in cell line HT-1080, which radial distribution is significantly shifted into the interior of cell nucleus in comparison to other cell lines. All telomeres of chromosomes 18 and 19 were found to exhibit higher occurrence of telomere associations in cells with ALT mechanism in comparison to health cells or cells with active telomerase as was expected. This conclusion was not found to be valid for telomeres of acrocentric chromosomes, probably due to influence of binding of these chromosomes to nucleolus. After calculation of average occurrence of associations of certain telomere with other telomeres of acrocentric chromosomes was found that these average occurrences are the highest in tumor cells HT-1080 with active telomerase. We also analyzed and compared in unsurpassed detail the telomere dynamics in living U-2 OS and HeLa cell lines varying in mechanism of telomere length maintenance in 3D space by time-lapse fluorescent confocal microscopy.