of utmost importance/the utmost importance

No difference in meaning. Both grammatically correct. The second is more commonly heard.

Technically, utmost is a superlative, like best, worst, most, least, largest, etc, and should be preceded by 'the', but many people ignore this.

Thank you.

Not only ignore, but phrases like "best practice", "worst case", "best efforts" are pretty standard now.
Best foot forward.

If you mean the omission of THE is standard, could you give me some example sentences?

Careful with the "standard". Of course I agree with contrex that the best, the worst, the ultimate, the utmost etc. is normal expression of a superlative, but sometimes and in certain phrases the "the" is omitted.

examples as requested:

I urged the team to use best efforts to achieve the result we wanted.
What we have here is a worst-case* scenario.
Use of best practice is the rule here, always. We don't tolerate sloppiness.

*the hyphen here, making a compound adjective, makes a difference and so is not a very good example of the point I was making. But it's a very commonly-heard phrase.

I would say that using the article 'the' is there to emphasize its unique, superlative quality. Without it, it seems to connote that the subject is among the very ~est.

Thanks to Mctag.

What's FBM's first language?

English. I teach it at university.

US or UK English?

Yes.




I'm of the US species originally, but I emphasize to my students that there are multiple Englishes. I also take care to (try to) teach them the differences among them and to be consistent in their usage in any given context.

No. I mean your first language; US or UK?

Every educated English native speaker can do both, after a fashion.
I have trouble with baseball terms.

US.