Purpose: Growth of intracranial fusiform aneurysms (IFA) may become clinically problematic through a mass effect or rupture. We investigated the growth rate and factors contributing to growth in asymptomatic untreated IFA. Method: As a retrospective review, we assessed patients diagnosed with asymptomatic IFA between August 2000 and September 2014, all untreated. No acute or symptomatic dissecting lesions were considered. Clinical and serial angiographic follow-up data were analyzed, defining growth as expansion > 2 mm in one or more dimensions. A binary logistic regression model and Kaplan-Meier method were applied for statistical analysis. Results: The mean follow-up in the 82 eligible patients was 47.7 months (range 12–190 months). Among them, 7 aneurysms (8.5%, 2.1% per aneurysm year) demonstrated growth (in any dimension). In univariate analysis, height and multiplicity of aneurysms emerged as significant factors in terms of growth. Height remained an independent risk factor in the binary logistic regression model, with receiver operating curves indicating a threshold of 6.9 mm initial height in determining IFA growth (area under the curve 0.804). Of the patients six (except one who underwent endovascular treatment) were observed during continued follow-up monitoring. All six lesions were stable in serial imaging tests, without further detectable growth or rupture (mean 33 months). Conclusion: Most (91.5%) of the asymptomatic and untreated IFAs studied proved to be stable, with no continued growth; however, because aneurysm height proved to be independently predictive of growth (lesions > 6.9 mm being at risk), periodic imaging is required in those left untreated. Growing but still asymptomatic aneurysms call for the utmost caution and care in decision-making.