AIM: To investigate regional variations in Chronic Kidney Disease (CKD) aetiologies and complications across KDIGO risk strata in Thailand, aiming to optimise screening and monitoring in resource-constrained settings. METHODS: Baseline data from the multicentre THAI-CKD cohort of adults with stages G3-G5 CKD from 41 hospitals were analysed. Demographic, clinical and laboratory data were collected. Causes of kidney disease, including chronic kidney disease of unknown aetiology (CKDu) and metabolic complications were examined across KDIGO glomerular filtration rate and albuminuria (G-A) categories, primary aetiologies, and geographic regions. RESULTS: Among 3371 participants (mean age: 69 ± 12 years; 55% male), stage distribution was G3a 20%, G3b 33%, G4 37% and G5 10%. Diabetic nephropathy (41%) and hypertensive nephrosclerosis (34%) were the most common causes, whereas CKDu accounted for 22% overall and was concentrated in earlier stages with lower albuminuria and in the Central (33%) and Western (24%) regions. Complications showed clear gradients across G-A strata: anaemia and metabolic acidosis increased with lower estimated glomerular filtration rate and higher albuminuria. Secondary hyperparathyroidism occurred across all stages and was most frequent in G5, whereas hyperphosphatemia was mainly observed in G5 and hyperkalaemia remained rare across all categories. The prevalence of complications also varied by primary aetiology and geographic region, and these associations remained significant after multivariable adjustment. CONCLUSION: This national cohort demonstrated pronounced regional and etiologic heterogeneity in CKD and revealed stage- and albuminuria-dependent patterns of metabolic complications. These findings support the use of KDIGO G-A staging and regional profiles to prioritise etiologic evaluation and tailor laboratory monitoring in low- and middle-income settings.