The author of Walking On Eggshells says about 25% of people with BPD also have narcissistic personality disorder. But that's gotta be only a guess. How can we know for sure if they tend to be invisible and never seek help. So may be that 25% is just from BPDs who were seen and also include a 2nd or 3rd PD in addition to? Dunno. How many there really are is any one's guess. But your on to some thing for sure because npd is common along side of higher functioning BPD. And who knows how common just some narcissistic tendencies are in BPD without it having to be an actual second diagnosis? One thing is certain. It's a big world out there and people are not fitting in so neatly to the boxes our experts want to put is in. I don't place much weight or faith in our psychiatric experts.